Renewed violence in the Yemeni capital killed at least nine people as street battles broke out between forces loyal to the regime and its opponents, medical and security officials said.
The officials said six people died in central Sanaa when government forces shelled thousands gathered for a protest there with mortars and rocket propelled grenades. Snipers on rooftops also targeted the protesters at Change Square, the epicenter of Yemen's seven-month-old uprising, and adjacent streets.
Three bystanders were killed by a mortar shell in Sanaa's northern Hassaba district, the officials also said. The district is home to several of the tribal chiefs who switched sides in March to join the opposition against the 33-year rule of President Ali Abdullah Saleh.
The latest deaths took to about a 100 the number of people killed in Sanaa and elsewhere in Yemen since Sunday, in the worst bout of bloodshed in months. The deaths also shattered hope that a cease-fire negotiated on Tuesday could be restored and significantly diminished the chances for a proposal by Yemen's Gulf Arab neighbors to end the crisis.
The Gulf plan, backed by the United States, provides for Saleh to step down in exchange for immunity and for the vice president to take the reins of power until elections are held.
Yemen's turmoil began in February as the unrest spreading throughout the Arab world set off largely peaceful protests in the deeply impoverished and unstable corner of the Arabian Peninsula that is also home to an al-Qaida offshoot blamed for several nearly successful attempts to attack the United States.
Saleh's government responded with a heavy crackdown, with hundreds killed and thousands wounded so far.
The officials who gave today's casualty toll spoke on condition of anonymity because they were not authorized to talk to the media. They said that scores of homes and stores across central Sanaa were damaged or caught fire as a result of random shelling blamed on government forces.
The shelling also ruptured many water tanks traditionally stored on rooftops of Yemeni homes, inundating the streets below. Sanaa has for weeks suffered from acute water and power shortages, forcing residents to rely on power generators and buy water extracted from wells and sold on a thriving black market.
Street battles broke out between armed tribesmen opposed to Saleh and their rivals in several locations across Sanaa on Thursday but there were no immediate reports of casualties.