Police fired live ammunition, tear gas and used water cannons to disperse demonstrators protesting outside a municipal building to demand the release of a fellow protester who was arrested on Saturday.

The clashes took place near Freedom Square where thousands of anti-government protesters have been camping since January to demand Saleh's overthrow. Police set two tents on fire in the square. Protesters hurled Molotov bombs and rocks at police.

In the capital Sanaa, seven explosions were heard on Sunday night in the district of Hasaba, the scene of week-long fighting between Saleh's forces and a rival tribe in which 115 people were killed, residents said.

There were no immediate details on the explosions, which appeared to have partially breached a truce between Saleh's forces and the powerful Hashed tribe led by Sadeq al-Ahmar in the bloodiest fighting since unrest erupted in January.

Ahmar condemned what he described as "Saleh's new massacre" against civilians in Taiz. Earlier on Sunday, his men handed back control of a government building to mediators as part of a ceasefire deal.