Tens of thousands of people took to the streets of Sanaa on Sunday demanding President Ali Abdullah Saleh's trial for crimes committed during his decades-long rule, hours before he is expected to make a speech.
The protesters, who set off on from Change Square, the epicentre of the pro-democracy movement in the capital, chanted "Freedom! Freedom! The people want the butcher tried!"
Their demand comes after the bloodiest week Sanaa has seen since mass anti-government protests calling for Saleh's resignation erupted in January, prompting fears of renewed clashes.
In all, more than 170 people, mostly unarmed protesters, have been killed in the capital since last Sunday.
Most of the casualties were anti-government protesters killed when security forces used artillery and gunfire and to disperse demonstrating crowds.
In Yemen's second largest city of Taez, three people were killed and three others were wounded in clashes early on Sunday.
The overnight fighting erupted between armed tribesmen who have thrown their support behind anti-government protesters and security forces loyal to Saleh.
Two tribesmen were killed and three others were wounded, a tribal source told AFP, requesting anonymity.
A medical official in Taez said a third man was shot early on Sunday by government troops.
The clashes came a day after Yemeni security forces in Taez, including the elite Republican Guard troops commanded by Saleh's son Ahmed, bolstered their deployment throughout the city and on its outskirts.
The beefed up military deployment came after Saleh's return to Yemen on Friday after a near four-month absence.
He flew in from Saudi Arabia where he received treatment for wounds sustained in a June explosion at his presidential compound.
Taez has been the scene of intense clashes between government troops and anti-government protesters since calls for Saleh's resignation first began.
In June, influential tribal leaders deployed armed men to protect the pro-democracy protesters in Taez, leading to regular firefights and bloody clashes between the two sides.
At least eight people have been killed there in the past week, six of them civilians, according to medical officials.
The latest protests came amid renewed calls by the United Nations, the United Stares and Gulf leaders for Saleh to step down and transfer power to Vice President Abdrabuh Mansur Hadi.
The Gulf Cooperation Council, the sponsors of the Gulf initiative that provides a road map for a peaceful transition of power in Yemen, have been rebuffed by Saleh, who has repeatedly delayed signing the initiative.
On Saturday, GCC ministers condemned the violence in Yemen and echoed US and UN calls urging Saleh to "immediately" sign the initiative.
They also called for "self-restraint, a complete and immediate ceasefire, and for forming a commission of inquiry in the latest events that have cost the lives of innocent Yemenis."
A UN Security Council statement on Saturday called on all sides to "reject violence, including against peaceful and unarmed civilians, and show maximum restraint."
"They called on all parties to move forward urgently in an inclusive, orderly and Yemeni-led process of political transition," it said.
Meanwhile, government forces, dissident troops and armed tribesmen, both pro- and anti-Saleh, remained heavily deployed throughout Sanaa, an AFP correspondent said, raising fears of renewed clashes ahead of Saleh's anticipated speech.
The official Yemeni news agency has said he would make "an important speech to mark the 49th anniversary" of the September 26, 1962 revolution that saw Yemen proclaimed a republic, although no appearance has been officially announced.
Saleh, who has been in power since 1978, traditionally makes his speech on the eve of the anniversary.