Tribal fighters ranged against Yemen's president Ali Abdullah Saleh have fought pitched street battles in Sanaa, the capital, killing more than 40 and raising the spectre of a civil war.
On Thursday, residents were fleeing Sanaa by the hundreds, hurriedly fastening possessions to the roofs of cars, hoping to escape the violence that has killed more than 70 people since Monday, Reuters news agency reported.
"We call on President Saleh to stop the fighting and answer the demand of the Yemeni people for an immediate and urgent abdication of power"
Yemeni opposition coalition
Fighters in civilian clothes roamed some districts and machine gun fire rang out sporadically.
Explosions could be heard in the capital near the protest site where thousands of people demanding Saleh's exit from power are still camped.
There were long queues at bakeries, banks and petrol stations, as residents tried to stock up on cash and food before fleeing to safer areas in the impoverished state.
"I'm going to Hudaida, I can't stay anymore after what happened last night. That was crazy. We are civilians and want to live in peace," Hani Zobeidi, a civil servant, said.
The fighting, pitting Saleh's security forces against members of the country's most powerful Hashid tribe, led by Sheikh Sadiq al-Ahmar, was the bloodiest Yemen has seen since protests began in January.
The Yemeni president ordered the arrest of Sheikh Sadiq following the deadly clashes.
In a statement issued on Thursday, Yemen's defence ministry said Saleh had ordered that al-Ahmar and nine brothers be brought to justice for "armed rebellion".
Dozens of people were killed in overnight gun battles in Sanaa, while the defence ministry said at least 28 people were killed in an explosion at an arms storage area.
A government official said that the headquarters of an opposition television station had been "destroyed", without giving details.
Sheikh Sadiq is the leader of the Hashid tribe, which includes Saleh's tribe, and has been a vocal opponent of the president, joining protesters in calling for him to leave power.
The Hashid tribe is one of two main tribal groupings in Yemen. Alongside the Baqil, it has played a leading role in politics for centuries.
|Hillary Clinton, at G8 summit, called on Saleh to step down [GALLO/GETTY]
According to leaked US cables, Sheikh Sadiq, and his brother Amid, have long wanted to replace Saleh.
And in March, another member of the clan - Yemen army general - Ali Mohsen al-Ahmar, also threw his weight behind the protesters.
G8 for Saleh's departure
Meanwhile, leaders of the Group of Eight (G8) powers attending a summit in France have called on Saleh to quit.
"We deplore the fighting that occurred overnight which was a direct result of the current political impasse, for which President Saleh has direct responsibility due to his refusal to sign the Gulf Co-operation Council (GCC) transition agreement," a French foreign ministry spokesman said.
The US, which has long considered Saleh as an ally in its fight against al-Qaeda in the region, called on the embattled Yemeni leader to quit.
Hillary Clinton, the secretary of state, said in Paris: "We continue to support the departure of President Saleh who has consistently agreed that he would be stepping down from power and then consistently reneged on those agreements."
The US has ordered all non-essential diplomats and embassy family members to leave the country.
Britain has also withdrawn diplomatic staff because of the deteriorating security situation in the country.
William Hague, the foreign secretary, said he was "appalled by the reports of yet more deaths in Sanaa'' and urged Saleh to step down.
Catherine Ashton, the EU foreign policy chief, urged all sides in Yemen to cease violence as she renewed a call for Saleh to transfer power.
"I deplore the loss of so many lives and injuries. I strongly call on all sides to exercise restraint and refrain from further violence," she said.
UN secretary-general Ban Ki-moon's spokesman, Martin Nesirky, said Ban was deeply troubled by the clashes in Sanaa and called for further peace efforts and an immediate end to the fighting.
No takers for GCC deal
The most recent bout of fighting erupted a day after Saleh pulled out for the third time from a deal mediated by Gulf Arab neighbours for him to quit and make way for a unity government.
Pressure has been mounting since February, when protesters inspired by democratic revolutions in Tunisia and Egypt began camping in squares and marching in their hundreds of thousands to call for Saleh to go.
His attempts to stop the protests by force have so far claimed the lives of more than 200 people.
The coalition of opposition parties that has sided with protesters and was due to sign the deal brokered by GCC held an emergency meeting on Thursday over what it called Saleh's "insistence on dragging Yemen towards civil war”.
"We call on President Saleh to stop the fighting and answer the demand of the Yemeni people for an immediate and urgent abdication of power," the coalition said in a statement.
Saleh had said on Wednesday he would make no more concessions to those seeking his departure.