December 4: The mass deportation of 3,000 Yemenis from Saudi Arabia is another hiccup in the long-running border dispute between the two countries.

Although there are echoes of 1990-91 (when some 750,000 Yemenis were summarily bundled over the border to emphasise the Saudi disapproval of Yemen's attitude to Iraq), officials in Sana'a are taking a more sanguine view this time. They acknowledge that the people concerned were not legally entitled to remain in Saudi Arabia and had been held in detention there for some time.

What prompted the Saudi move was a bilateral meeting in Sana'a a few days earlier which had been intended to clarify some outstanding questions on the border issue.

The extreme western end of the border was defined in 1934 by the renewable Treaty of Ta'if. The remaining 1,000 miles or so to the east have never been formally defined, though a frontier known as the "Como Line" was provisionally agreed between President Salih and Prince Sultan at a meeting in Italy in 1997.

The latest dispute centres on the line set by the Ta'if treaty which, according Yemen, the Saudis are seeking to "improve" for security reasons. The treaty gave Yemen most of the mountain-tops and, theoretically, a military advantage in any conflict. A look at the text of the treaty shows that there is plenty of scope for argument about where the line lies, since it is defined by reference to various geographical features and tribal territories rather than precise co-ordinates. There are, apparently, piles of stones on the ground marking the boundary but these have been know to move mysteriously from time to time.

Last week's seven-hour meeting in Sana'a was intended to fix the position of the Ta'if line once and for all, in a more scientific way. It was at this point that whole mountains, not just piles of stones, began to move.

The Saudis were keen to shift the border away from high ground and denied that Jabal Sar, a peak at the eastern end of the line, was actually known by that name. They insisted that Jabal Sar was a much smaller hill six kilometres to the south. There have been similar disputes before, elsewhere along the Ta'if line - notably at the Red Sea end in 1998.

The Yemenis appear to have made some concessions to address Saudi concerns about security. The Ta'if treaty made provision for a 5-km demilitarised zone one either side of the line [Article 5] which Yemen has offered to extend to 20 km to take account of the longer range of modern weapons. This was the distance agreed a few years ago in the border settlement between Yemen and Oman.

Last week's expulsion of Yemenis from Saudi Arabia is a reminder of another issue regarding the Ta'if treaty. Until 1990, northern Yemenis were allowed to enter the kingdom on terms which were easier than those for nationals of other countries (including the PDRY). They had no need for a Saudi sponsor, and were allowed to own businesses without the customary Saudi partner. In Sana'a's view these privileges were not merely a favour bestowed by the Saudis but had a legal basis: letters exchanged by the Saudi and Yemeni leaders in 1934 at the signing of the Ta'if treaty can be interpreted as allowing relatively unrestricted Yemeni entry into the kingdom. Over the years, Sana'a has made a point of interpreting the letters in this way and has regarded them as an integral part of the treaty.

The latest flare-up between the two countries does not look unduly serious. Most probably it marks the final push in a dispute where the two sides are not actually very far apart. But that does not mean it will soon be resolved. The problem is how to move it on and close the deal. Yemen says bilateral talks have reached a dead end and is pushing for international arbitration. Under a covenant attached to the Ta'if treaty, both parties agreed to refer disputes to arbitration within one month of receiving such a demand from the other side. As yet, Yemen has not made a formal demand but the Saudis are saying they will reject arbitration anyway.

THE CULPRIT

SO NOW we know. As in all the best detective stories, the culprit was the person that nobody (apart from the brilliant detective) ever suspected. According to the official version, Abdullah al-Omeiri, owner of the City Center supermarket, destroyed it himself.

Mr Omeiri had debts and tried to sell his business to pay them off, but nobody would give him the asking price. So he decided to set fire to it, hoping to claim $2.5 million from the insurance company.

He recruited seven helpers - among them his son and an Indian engineer as technical adviser. To make sure it burned well, they used 15 cylinders of gas and 29 cans of petrol. Actually, it went far too well and Mr Omeiri died in the blast, along with the innocent guard at a building nearby. A dozen others were injured - including some of his accomplices.

Possibly Mr Omeiri was so worried about his debts that he could not think clearly, but it is difficult to see how he expected to get away with it when so many people knew of his plan.

Earlier, the Islamic Army of Aden-Abyan had claimed responsibility for the blast, just as it did when a man in the old market of Sana'a killed six people because he felt cheated over the price of a $31 watch. It now appears that both incidents were unrelated and non-political. But perhaps they did have something in common. At opposite ends of the social scale - rich and poor - they may tell us something about the depth of Yemen's economic problems.

EXPERTS BLAME GAS

September 2: The blast that killed at least two people, totally destroyed Yemen's largest supermarket, damaged property over a quarter-mile radius and woke up most of Sana'a at 2am on August 28 was not caused by a bomb or explosives, according the army newspaper, "26 September".

Scientific analysis has established that the cause was a large quantity of gas, the paper says. It adds, however, that the incident was "100% criminal" - though without any political or terrorist motive.

The paper says that the gas was stored in cylinders at the supermarket for use in its restaurant, and some was used specially for refrigeration equipment.

According to a report by forensic and explosives experts, the paper says, no trace of explosives was found at the scene. Investigations are continuing and some "important and surprising" facts will be disclosed shortly, it adds.

Meanwhile, a government source has told Yemen Gateway that the explosion was "not even" the result of a business quarrel or action by a disgruntled employee, and that details will be made known on Saturday.

WHODUNNIT?

August 30: Three explosions in three days. The obvious question is: are they connected? Abu Hamza al-Masri, London-based friend and mouthpiece of the Islamic Army would like us to think so. In line with a policy of claiming the credit (or blame) for any untoward incidents in Yemen, he says that all three were the Islamic Army's handiwork.

The Yemeni government, on the other hand, denies any connection and maintains that the Islamic Army does not exist - except, perhaps, in the form of a publicity machine.

The reality is that the Islamic Army was never an army as such, though it had weapons and  a training camp. Essentially, it was a small, loosely-connected group of troublemakers from various countries. Following the arrest of its leader, Abu al-Hassan, and others last December and January, its strength has been further diminished.

Investigations may or may not cast more light on the recent explosions, but it is worth considering the targets and the likely motives of attackers.

On August 26, late at night, a small bomb (or possibly two) exploded in Zinjibar near the prison. Damage was slight and nobody was hurt. Southern Yemen has seen many similar incidents near government buildings, apparently aimed at causing alarm and timed to minimise casualties. Zinjibar is on the Islamic Army's home patch and the trial of Abu al-Hassan and his accomplices took place there - so it's a logical and likely target as far as the Islamic Army is concerned. Significantly perhaps, the official denial of an Islamic Army connection (as reported by Reuters) referred to the explosions in Sana'a and Aden, but not specifically to Zinjibar.

On August 27, again late at night, a device described as a time bomb exploded in the Tawahi district of Aden, slightly damaging the back wall of the National Bank. Again, nobody was hurt. This was conceivably the work of the Islamic Army, though there is nothing so far - other than Abu Hamza's claims - to suggest that it actually was. Other terrorist groups are active in the area, and any of them could be responsible.

Unlike these minor incidents in the south, the explosion in the Hadda area of Sana'a on August 28 was massive. It is unlikely that the Islamic Army possesses the quantity of explosives involved or, if it did, that it would use them all at once to destroy a supermarket.

There is little doubt that the "City Center" supermarket was the intended target but, in a district full of politically symbolic buildings, it is difficult to see why the Islamic Army would choose to attack a shop - even if it was the biggest and best supermarket in Yemen.

The most plausible theory advanced so far - though at present it is only a theory - is that the attack was the result of a business feud. The picture will become clearer when the following questions have been answered:

• Why did the owner, Abdullah al-Omeiry, and his accountant go to the building shortly before the explosion at 2 am? Was it, as reports suggest, just to do a bit of late-night book-keeping?

• Did Mr Omeiry, as some reports suggest, receive a phone call at the supermarket 20 minutes before the explosion and, if so, what was it about?

• What were Mr Omeiry's social and business connections? Did he have any enemies?

• Why the discrepancy over the number of casualties? Official sources say two people died, including Mr Omeiry. The Yemen Times says there were at least three deaths - Mr Omeiri and two guards at neighbouring buildings. What happened to the six employees of the supermarket who were thought to be sleeping in the basement?

• Why did the authorities not carry out an inch-by-inch search of the wreckage for clues? Instead, a rapid clear-up operation began. Within 24 hours, according to the Yemen Times, all the wreckage had gone, leaving "an open and empty piece of land".

If, as seems likely, the supermarket explosion was not the work of the Islamic Army, the authorities may feel inclined to sigh with relief. But they should be worried if it turns out that  individuals have been able to obtain large quantities of explosives and should ask themselves how that can be prevented in future. Secondly, if the "business feud" theory is substantiated, they should be worried about its impact on economic confidence. Ultimately, attacks on businesses may prove more damaging to Yemen, in the eyes of foreign investors, than anything the Islamic Army is capable of doing.

TERRORISM BY FAX

August 17: Has the Islamic Army really carried out two horrifically bloody attacks in the space of 10 days, or is it just bluffing? Abu Hamza al-Masri, ever ready to oblige, faxed a statement on the Islamic Army's behalf claiming responsibility for both the grenade attack in Sana'a and the crash of a military helicopter in Hadramaut. The mujahideen, he would have us believe, are everywhere.

The cause, apparently, is the threat of execution hanging over Abu al-Hassan al-Mihdar ("commander" of the Islamic Army) and another man for their part in the kidnapping of 16 western tourists and the killing of four of them. On August 4, a court rejected Abu al-Hassan's appeal - though the legal process is likely to continue through the Supreme Court and finally to President Salih himself.

Just a few hours after the appeal ruling, a man set off a grenade and opened fire in the old salt market of Sana'a, killing six people and wounding more than 40. Because of the timing, it appeared as though the Islamic Army's threat of reprisals might have been fulfilled.

At this point, instead of damping-down speculation, the authorities fuelled it by issuing confused and contradictory statements. First, they denied that the attack had any political motive. Later, the official Saba news agency described the culprit as a "corrupt extremist" and a police spokesman claimed that six more suspects had been caught, "posted on rooftops carrying weapons". Later still, on August 7, the interior minister said the attack was non-political and had arisen from an argument about the sale of a watch worth $31.

With the waters suitably muddied by the government's own information machine, the Islamic Army was able to step in with its triumphant claim. But in terms of the Islamic Army's usual strategy, an attack on ordinary poor folk in a Sana'a market makes no sense. What's the point? And if the Islamic Army really was involved, why did it take so long to say so?

Ten days after the grenade attack, a military helicopter crashed in Hadramaut province, killing 17 people, including a number of very senior army officers. The crash was variously attributed to a technical fault or bad weather.

However, the statement issued through Abu Hamza said that a member of the Islamic Army, Ali Mohammad Abu Abdulrahman, had "martyred" himself by blowing up the helicopter.

At first sight, this claim looks a little more credible. The victims were the sort of people the Islamic Army might be expected to target. The naming of a "martyr" gives the claim an authentic touch - though it may be totally spurious. (If anyone has information about the man, please let us know.)

On the other hand, genuine accidents of this kind are not particularly surprising in Yemen. Readers may be interested to study the picture of the wreckage published in al-Ayyam newspaper. The remains of the helicopter seem to be spread over a small area, which does not immediately suggest a large mid-air explosion.

Even if there is no truth in the Islamic Army's claims, the Yemeni government may have a difficult time convincing people that its version of events is correct. The mujahideen, whatever their military capabilities, certainly know how to exploit publicity when an opportunity arises.

DEATH SENTENCES

THE THREE kidnappers sentenced to death in Zinjibar trial will - if the sentences are carried out - be the first to be executed since the death penalty for kidnapping was introduced by presidential decree in August 1998. (See list of recent executions.)

Those sentenced to death are Zein Al-Abidine al-Mihdar ("Abu al-Hassan"), Abdullah Salih al-Junaidi, Salih Abu Huraira, an Algerian. Ahmed Mohammed Atif was sentenced to 20 years in prison, but his brother was acquitted. (See our special section for details of the kidnappers and the kidnapping.)

Previous kidnappers have generally gone unpunished, though this is the first case in which foreign hostages have died.

In this case, as in earlier ones, the Yemeni government is torn between the need to take a firm line on terrorism and the need to avoid further trouble from the kidnappers' tribal and religious supporters. There have been reports of strenuous efforts being made by the authorities to win over key members of the kidnap leader's tribe.

In ordinary murder cases, under Islamic law, relatives of the victims can request clemency. But it is not yet clear whether the death sentences in this case apply only to the killing of four of the hostages, or whether they apply also to the kidnap itself; if so, the clemency rule might not operate.

Even after the trial it is uncertain precisely who killed the four hostages: it is possible some of them were caught in crossfire between the kidnappers and security forces, or that some of them (as suggested by the accused) were killed by one of the kidnappers who also died in the shoot-out. The leader, Abu al-Hassan al-Mihdar, told the court that he gave instructions to kill male hostages if the Yemeni troops opened fire - but two of the dead were women.

Those sentenced have a month in which to appeal and, in any case, the constitution requires any executions to be personally approved by the president.