At least 12 people were killed in fierce clashes in Sanaa between President Ali Abdullah Saleh's troops and rival forces in escalating violence on Saturday, a day after the UN Security Council urged the embattled leader to hand over power.
Witnesses and AFP correspondents in Sanaa said explosions were heard throughout the day in Sanaa, and massive plumes of smoke and fire were seen rising from several neighbourhoods where opposition forces are stationed.
An AFP correspondent said ambulances raced out of the Hasaba district that is home to tribal chief Sheikh Sadeq al-Ahmar and his brothers, whose tribesmen have been battling Saleh's troops for weeks.
The war-torn district has become a ghost town, sealed off by Saleh's troops, with no one allowed in or out, according to an AFP correspondent on the scene.
Abdul Qawi al-Qaisi, who heads Ahmar's office, told AFP that two of the tribal chief's men were killed and 27 others were wounded in the clashes, which became even more intense in the evening.
Medical officials said five civilians were killed during intense shelling north of the Hasaba district in Sanaa.
And five dissident soldiers were killed and dozens of others were wounded, including unarmed civilians, in clashes and shelling throughout the capital, they added.
In Taez, Yemen's second-largest city, clashes erupted between armed men who claim to protect protesters, and pro-Saleh troops, injuring at least three people, pro-democracy activists in the city told AFP.
Dissident General Ali Mohsen al-Ahmar, who defected in March in support of anti-government protests sweeping the country, blamed Saturday's violence on Saleh and called on the international community to intervene.
He urged the international community to take "decisive and urgent" action to force Saleh from power or risk "a civil war."
In a statement, the general accused the president of giving orders to his sons and relatives who command Yemen's elite military forces to "attack with all weapons ... and cleanse Hasaba district and destroy everything" in their path.
In the Change Square area, where thousands of protesters have been camped out calling for Saleh to quit, fierce clashes erupted between government troops and defected soldiers loyal to the dissident general.
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The general and tribal chief, both former staunch allies of Saleh, are now his arch-rivals, having thrown their support behind the nationwide protests which have triggered Yemen's political crisis.
Saturday's violence came a day after the UN Security Council unanimously passed a resolution that "strongly" condemns the deadly government attacks on demonstrators and backs a Gulf plan for Saleh to end his 33 years in power.
Several hundred people have been killed since the protests against Saleh erupted in late January.
Saleh has for months refused to buckle under intense local, regional, and international pressure to resign and hand power over to Vice President Abdrabbo Mansour Hadi.
Under a Gulf Cooperation Council (GCC) initiative, Saleh would step down within 30 days of signing the deal handing him and his family immunity from prosecution, a controversial component of the transition plan.
London-based human rights watchdog Amnesty International said Saturday a call for accountability in Yemen from the UN was "doomed to fail if officials are granted immunity."
"The UN Security Council's efforts and those of the GCC ... are to be lauded, but President Saleh must not be given immunity as a prize for stepping down," Malcolm Smart, Middle East and North Africa director, said in a statement.
"Such immunity would obstruct justice for hundreds of deaths during months of protest in Yemen," the statement said.
Yemen's Nobel Peace Prize winner Tawakkul Karman also criticised the UN resolution for supporting the immunity clause.
"They have to discuss the ousting of Saleh and how he has to be handed over to the International Criminal Court as a war criminal," Karman said outside the UN in New York where she has been calling for a tougher stance on Saleh.
Calls for more decisive UN action have increased, with tens of thousands of pro-democracy activists urging the world body to step in and stop the violence engulfing the impoverished country.
The protesters have also increased their calls for Saleh to be tried before the world court.
Britain's UN ambassador Mark Lyall Grant said the resolution does include some "tough messages" for Saleh and that there would be "no impunity for human rights abuses," despite its clear support for the GCC initiative.