Western and Arab diplomats were airlifted out of the United Arab Emirates' embassy in Yemen Sunday, after supporters of President Ali Saleh surrounded and besieged the embassy. The Gulf Cooperation Council also withdrew its U.S.-backed plan for the peaceful resignation of the Yemeni president, after he backed out of signing it for a third time.

The Christian Science Monitor called the siege "an exquisitely timed show by gunmen loyal to President Ali Abdullah Saleh," which "staved off" the signing of a transition plan. Saleh refused to sign over a protocol complaint, namely that opposition leaders refused to attend a ceremony for the transition at the presidential palace.

The siege has also raised strong questions about U.S. aid to his regime and the ever-increasing possibility of civil war. Several senior politicians and military units have defected and joined the opposition, pitting tribe against tribe. Tension on the streets of the capital Sanaa has been high since protests began in January, with increasing anger following a brutal government crackdown.

"The level of restiveness in the military is as high as it is in the street and there's no way of guaranteeing their loyalty," says Abdul-Ghani al-Iryani, a political analyst based in Sanaa. "In Yemen we don't really have a military as an institution, we have tribal factions in uniform, many of whom can be bought over to the other side. If he [Saleh] chooses to have a military showdown it will definitely be the end of this regime but also a lot of bloodshed."