As an end to the 33-year reign of President Ali Abdullah Saleh drew near violent clashes have erupted in the capital leading many to fear Yemen is headed from the brink of peace into civil war.

Last week Saleh announced he would not return to Yemen and authorized his deputy, Vice President Abd-Rabbu Mansour Hadi, to negotiate a transfer of power agreement in his stead.

But skirmishes between protesters and security forces snowballed into pitched street-battles between loyalist and dissident troops with exchanges of live fire and rockets throughout the city by mid-week.

At least four civilians were killed in crossfire between Republican Guard troops commanded by Saleh's son Ahmed, and dissidents loyal to General Ali Mohsen Al Ahmar, witnesses and medics said.

On Tuesday the fragile policy of mutual avoidance between loyalist and dissident troops collapsed when protesters laid siege to a republican guard installation in Sanaa, prompting live fire from the defenders.

The gloves came of when rumors a Gulf-sponsored peace deal failed due to what its sponsors said were the soaring tensions between troops loyal to Yemeni President Ali Abdullah Saleh and opponents of his regime.

A truce negotiated declared by the vice president after Tuesday's fighting collapsed early on Wednesday. It is unknown if opposition leaders and officials in the regime continue to discuss a transfer of power amid the fighting.

Thursday's deaths bring the toll in the capital to 89 since Sunday.