SANAA Supporters and opponents of Yemeni President Ali Abdullah Saleh were expected to hold large rival demonstrations on Friday after a week of clashes in the capital threatened to tip the country into civil war.
More than 40 Yemenis were killed in Sanaa on Thursday in the fourth day of fighting since the collapse of a Gulf-brokered agreement for Saleh to bow to widespread demands to step down and bring an end to four months of unrest.
Friday prayers have been a traditional rallying point for opponents and supporters of Saleh, whose country has become the poorest in the oil-rich region during his three decades in power.
Residents have been streaming out of the city by the thousands to escape the violence. Others stocked up on essentials and waited in trepidation for what the day might bring.
The fighting, pitting Saleh's security forces against members of the powerful Hashed tribe led by Sadiq al-Ahmar, was the bloodiest Yemen has seen since protests began in January.
More than 80 people have been killed since Sunday. Machinegun fire rattled across the city on Thursday and sporadic explosions were also heard near the protest site where thousands of people demanding Saleh's departure are still camped.
The Yemeni protest movement, born out of the "Arab Spring" that led to the ouster of the long-standing leaders of Egypt and Tunisia, used social media sites including Facebook to call for a "Friday of Peaceful Revolution" rally.
One telephone text message said the rally: "... is to stress the peacefulness of the revolution and rejection of efforts to drag the country into a civil war."
Ahmar tribal leaders including Sadeq al-Ahmar and Hamid al-Ahmar have thrown their weight behind the protesters.
Saleh supporters plan their own "Friday of Law and Order" rally just a few kilometres away and have sent out a telephone text message saying their rally will: "condemn the crimes against our rights and the rebellion against the country".
There are worries that Yemen, already teetering on the brink of financial ruin, could become a failed state that would undermine regional security and pose a serious risk to its neighbour Saudi Arabia, the world's biggest oil exporter.
The United States and Saudi Arabia, both targets of foiled attacks by a wing of al Qaeda based in Yemen, are concerned any spread of anarchy could give the global militant network more room to operate.
Dozen of armed men believed to be from al Qaeda stormed the city of Zinjibar in the southern flashpoint province of Abyan, routing out security forces and setting off blasts in several buildings, residents said.
The army previously retreated from the city in a battle with militants in March but later regained control.
Saleh has warned his ouster would be a boon to al Qaeda but the opposition, which includes Yemen's Islamist party, accuses him of exploiting militancy for foreign backing and argues it would be better placed to fight the group.
BRINK OF RUIN, ANARCHY
As the situation deteriorated, foreign embassies reduced staff and urged their nationals to leave.
Leaders of the Group of Eight powers meeting in Deauville, France, 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 GCC transition agreement," a French Foreign Ministry spokesman said, referring to the Gulf Cooperation Council.
The United States, which long treated Saleh as an ally against al Qaeda, also said it now wanted him to go. U.S. Secretary of State Hillary Clinton said he had "consistently reneged" on agreements to step down.
Tribal leader Ahmar told Reuters there was no chance for mediation with Saleh and he called on regional and global powers to force him out before the country of 23 million people plunges into civil war.
"Ali Abdullah Saleh is a liar, liar, liar," said Ahmar. "We are firm. He will leave this country barefoot."
Saleh said on Wednesday he would not bow to international "dictates" to step down and leave Yemen.
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 260 people.
(Additional reporting by Mohamed Sudam and Khaled al-Mahdy in Sanaa and Erika Solomon in Dubai; Writing by Angus MacSwan; editing by Mark Trevelyan and Philippa Fletcher)