Yemen's president launched air strikes yesterday in a rearguard action to stop the capital city, Sana'a, falling to tribal fighters seeking to overthrow him.
Pilots loyal to President Ali Abdullah Saleh attacked militiamen 45 miles from Sana'a, as they attempted to seize three military posts on their march to reinforce Sadiq al-Ahmar, a tribal chief whose forces have seized control of key buildings in the capital.
At least 19 tribesmen were killed but the president's fragile position forced him to seek a truce with Mr Ahmar.
Once an ally of the president, Mr Ahmar has joined a number of defectors supporting a movement to demand Mr Saleh's resignation.
The president's hopes of inflicting a quick defeat on his rival were dashed as his Republican Guard lost control of several government buildings in the city. More than 120 people have been killed.
Western leaders meeting at a G8 summit in France have urged Mr Saleh to sign a deal that would see him hand over power within 30 days in exchange for immunity from prosecution.
UN officials fear the fighting could cause an implosion in a volatile state that has become a major breeding ground for al-Qa'ida.
Rupert Colville, a spokesman for the UN High Commissioner for Human Rights, said: "We are deeply concerned that the government may be pushing the country close to the brink of civil war."
Mr Ahmar said he was ready to abide by a truce, but suggested he did not believe the president would maintain peace for long.
"If the Saleh regime wants a peaceful revolution, we are ready for that," he said. "If he chooses war, we will fight him."
There was also speculation that Saudi Arabia, whose support for Mr Saleh has been crucial, has told him he has no choice but to stand down. Earlier yesterday, Sadiq al-Ahmar, leader of Yemen's most influential Hasid tribe, said he reached a ceasefire agreement with the government to end a gun battle in a suburb of the capital that left dozens dead.
Mr Ahmar told thousands of people gathered in Sana'a that the ceasefire was brokered through tribal mediation. "It seems the agreement is working," Mohammed al-Mutawakil, a leader in the opposition coalition known as Joint Meeting Parties, said.
He said that under the truce, both the government and Mr Ahmar would pull their armed forces out of Hasaba, a district in northern Sana'a where the worst of the fighting has taken place since May 23.
The announcement came as hundreds of thousands demonstrated in response to a call by opposition leaders for peaceful rallies that will underscore their opposition to the kind of violence that has gripped the capital. (© Daily Telegraph, London)