Battles between Yemen's most powerful tribal group and sections of the military have resumed in Sana'a this morning, and tribal fighters appear to control part of the capital, including the interior ministry building.

Tom Finn, who is on the spot, reported yesterday's events for the Guardian. Jane Novak, on the Armies of Liberation blog, adds some more details.

The picture is still very confused and a lot of unconfirmed and probably unreliable information is circulating on Twitter. It is beyond any doubt, though, that the situation in Yemen is now extremely grave.

After refusing to sign the GCC's "transition agreement" on Sunday (which required him to step down), President Saleh warned of civil war and now seems bent on fulfilling his prophecy.

It is difficult to imagine what Saleh's game plan might be – assuming that he has one. Viewed from outside, his chances of re-establishing his authority and restoring order are virtually nil, so we may simply be watching the flailings of a desperate man.

Alternatively, he may be hoping to persuade Yemenis that he is the only person who can save them from catastrophe (a catastrophe, incidentally, that is largely of his own making). Whether they will buy that, after all that has happened, remains to be seen. If they don't, the turmoil could be bloody and prolonged.

Posted by Brian Whitaker, 25 May 2011