There has been a sharp escalation in violence in Yemen overnight, where government forces have sent warplanes to bomb tribal groups demanding the president’s removal. President Ali Abdullah Saleh came close to signing a deal to step down last Sunday, after nearly 33 years in power, but he baulked at the last minute, provoking a new outburst of anger on the streets. Now both sides of government and the United Nations have voiced fears of an all-out civil war as the mass protests that erupted four months ago spiral into full-scale violence. One of the country’s biggest and most powerful tribes, the Hashid, joined protesters on the streets on Monday, a day after Mr Saleh had again rejected the deal to relinquish power. Hashid fighters have taken on security forces from the president’s own Republican Guard, in street battles that some reports say have left at least 100 people dead in the past five days. The tribe’s leader, Sheikh Sadiq al Ahmar, was once one of the president’s staunchest supporters. Mr Saleh himself comes from a tribe related to the Hashid. But as the protests against him in recent weeks gathered momentum and the president repeatedly dug in, Sheikh al Ahmar has turned against him. « We wanted a peaceful revolution, » he said. « But Ali Abdullah Saleh and his sons and loyalists want war. We won’t allow him to turn this into a civil war. He attacked our house but we are steadfast, now there is mediation between us to stop the war. » For now the Hashid tribe has agreed to a ceasefire, although it says it is still prepared for war. But in the past 24 hours, the violence has spread outside the capital, and taken on a whole new dimension. A second tribe has seized a military camp of the Republican Guard in Naham province, north-east of the capital Sanaa. In response, Mr Saleh’s forces sent warplanes to carry out air strikes against them. In the space of a few hours, more than a dozen people were reportedly killed. « Forty miles outside Sanaa almost 20 people have been killed in the last couple of hours, » Hakim al Masmari, the editor of Yemen’s Post newspaper, said. « Government attacks against the tribes in Naam. So in the capital it’s calm. But outside Sanaa, the outskirts, it’s very strong right now, casualties there, and the injuries are over 70 until now. » All sides in this conflict are now talking of civil war. Even the United Nations has voiced alarm at the escalating violence, given just days ago the president was so close to an agreement to step down. « We are deeply concerned that the government may be pushing the country close to the brink of civil war, » UN Human Rights Commission spokesman Rupert Colville said. The president has blamed his opponents for the escalation of violence, but in recent days he has not ruled out returning to negotiations. « I will transfer authority peacefully if they come to the dialogue table, » he said. If he does not, the predictions of war may well become reality.