A Yemeni activist says police fired tear gas and live ammunition at protesters calling for the ouster of the country's longtime president, injuring 45 people in a southern port town.
Monday's violence took place in Hudaida on the Red sea, where thousands rallied demanding President Ali Abdullah Saleh step down.
Activist Riyadh Al Absi says 45 were hurt, including 12 protesters wounded by bullets fired by plainclothes policemen. He says police used batons to beat protesters who responded by throwing stones.
Yemen has been wracked by protests since mid-February over the country's lack of freedoms and extreme poverty.
Also on Monday, several top figures and lawmakers who defected from Saleh's ruling Congress Party set up a new opposition party.
Earlier, witnesses said clashes on Monday had wounded at least 15 people when police fired shots and protesters responded by hurling rocks, witnesses and doctors said.
Residents said plain-clothes police armed with bats, pistols and stones, attacked thousands of protesters who had marched into the streets moving out of the square.
In Focus:Unrest in Middle East
In addition to the 15 people who were wounded, two were shot and several others were beaten or hit with stones, doctors had said.
Wtnesses said protesters retreated back to their camp after the clashes, and the streets returned to calm.
The protesters had been camped out in the square for weeks in demonstrations calling for the end of President Ali Abdullah Saleh's 32-year rule.
Tensions have run high across the deeply impoverished Arabian Peninsula state, where half the country's 23 million people are armed, as transition talks between the opposition and the government stall.
Protests which gather tens of thousands of people almost daily have now run into their third month.
No major breakthrough came of a meeting between opposition leaders and foreign ministers of the Gulf Cooperation Council in Saudi Arabia Sunday night.
The Gulf Arab states have offered to mediate for Yemen, but the opposition wants guarantees of a quick handover of power and a removal of Saleh from his post