Saudi newspapers are continuing to portray Thursday night's rioting in the holy city of Madina as an outbreak of youthful vandalism. Meanwhile, police are claiming it was triggered by "an argument between teenagers during a football match".

Eight hundred people are said to have taken part in the riot; windows were smashed, about 38 cars were destroyed or damaged and an unknown number of people – including three security officers – were injured, according to published reports. The sabq.org website has a series of pictures, though they mainly show bystanders.

Today's Arab News reports that the area affected is still being guarded by 10 teams of special security forces, 60 patrol policemen and 300 security officers "to prevent further violence between the two groups". Thirty-eight people are said to have been arrested, "from both sides".

The kingdom's mainstream media have gone out of their way not to mention the sectarian nature of the riot, though it must be obvious to their readers that the trouble occurred on the night of Ashura, when Shia Muslims mourn the martyrdom of the Prophet's grandson at the battle of Karbala – an event that lies at the heart of the Sunni-Shia schism. Al-Riyadh newspaper did give a small clue, though, when it  blamed the rioting on "young zealots who were wearing black clothes" (a reference to the Ashura mourning rituals).

According to Shia sources, the violence in Madina started when a large group of Sunni extremists from the Asbaa district (which is mostly Sunni) attacked Shia Muslims in the Qabaa district with sticks and stones.

In many ways, Madina is a microcosm of the kingdom's sectarian problem, in which the Shia communities (about 10% of the population) have been marginalised and discriminated against over many years. The issue is generally considered so sensitive that it can't be discussed in public, and increasingly it has become linked with fears about Iranian influence.

As well as being a major centre for Sunni Islam, Madina is home to a large and long-standing Shia community. It is also home to the Islamic University, founded by a royal decree in 1961, which has around 7,000 students and is regarded as one of the world's main training centres for Salafi preachers.

Another bone of contention in the city is the Baqi' cemetery where the Prophet and a number of his companions are buried. In 1925, King Abd al-Aziz ordered the destruction of various mausoleums on the site – in line with Wahhabi doctrine which prohibits "grave worshipping" and revering the dead. Shia Muslims resented this and still commemorate the demolition with Yaum-e Gham (the "Day of Sorrow").

Shia visits to the cemetery have been contentious in the past. Last year there were clashes between Shia pilgrims form Qateef on one side and Saudi police and Sunnis on the other.

Women are also normally banned from the cemetery though in 2008, for the first time, King Abdullah permitted a group of female Iranian pilgrims to visit it.

Posted by Brian Whitaker, 19 Dec 2010.