More than 20 Yemeni civilians, government troops and dissident soldiers were killed in overnight violence after President Ali Abdullah Saleh's latest pledge to step down, medics said on Wednesday.
The deaths in the capital Sanaa and the country's second largest city, Taez, came after Saleh told the US ambassador to Yemen he would sign a Gulf-brokered power transition plan to step down within 30 days.
The violence flared on Tuesday as the government's declaration of a truce with rival forces failed to materialise.
A government statement released on the official state news agency said two civilians were killed Wednesday in shelling of residential areas in Sanaa, blaming anti-government forces for the deaths.
In a separate statement on the defence ministry website, the government said nine of its soldiers fighting tribesmen and rival forces loyal to dissident General Ali Mohsen al-Ahmar were also killed.
Medical officials, meanwhile, said the overall death toll from violence from Tuesday night to Wednesday morning had reached 21, including a woman and her infant child who died in Taez when their house was struck by shells.
Residents said government troops had been bombarding the city since Tuesday.
In Sanaa, at least seven armed tribesman loyal to powerful Sheikh Sadeq al-Ahmar died in clashes overnight in the Hasaba district, home of the chief and his extended family who have been battling government troops for weeks.
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In a protest over the recent deaths of at least three women and three children, hundreds of women burned a pile of veils in a message to the country's tribes to step up their protection of civilians from Saleh loyalists.
"The killing of women is shameful and disgraceful," the women chanted as they doused a pile of scarves with gasoline and set them on fire.
"To the Yemeni tribes we say: 'Your sons and daughters are being killed in the streets and you stand on the sidelines silent, watching,'" they said.
In a separate protest across town, several hundred female pro-Saleh supporters marched on the United Nations building in Sanaa, waving pictures of Saleh and chanting "the people want Saleh."
The women delivered a letter to UN delegates demanding an "end to the terrorist acts" they said were being carried out by Sadeq's tribesmen and Mohsen's forces.
On Tuesday, the government declared a truce with Sadeq and Mohsen's forces, but within minutes of the announcement, gunfire and explosions were heard throughout the city.
The violence erupted as the US State Department said Saleh had pledged to sign a Gulf Cooperation Council initiative and step down. Saleh, who has ruled Yemen for 33 years, has repeatedly failed to fulfil pledges to resign.
Yemen has witnessed one of the longest and bloodiest uprisings of the "Arab Spring," with hundreds of Yemenis dead and thousands more wounded since January.
Saleh has for more than nine months refused, despite intensifying regional and international pressure, to heed the call of the tens of thousands of Yemenis who have held daily protests demanding his resignation.
The political stalemate has crippled the Yemeni economy, weakened the central government and prompted defections from Saleh's staunchest allies.
Mohsen and Sadeq, once Saleh loyalists, are now his enemies having thrown their support behind the protest movement as their troops battle Saleh's forces in increasingly deadly street clashes.