Police on rooftops have wounded at least 100 protesters in Yemen when they fired live bullets and tear gas.
Sunday's violence, which left one dead in a southern province, was the latest evidence that month-long protests demanding the resignation of the country's long-time leader were spiralling out of control. The wounded had been camping out near Sanaa University.
Embattled president Ali Abdullah Saleh has resorted to increasingly violent tactics to try to put down the burgeoning uprising against his 32-year rule, deploying dozens of armed supporters on the streets in an attempt to intimidate protesters.
Wielding clubs and knives, police and regime supporters described by protesters as government-sponsored thugs attacked activists camped out near Sanaa university, said Mohammed al-Abahi, a doctor in charge of a makeshift hospital near the university.
Among the 100 wounded in Sanaa, more than 20 suffered gas inhalation, and one was critical after being struck with a bullet, the doctor said.
In the main square and in surrounding streets, eyewitnesses spoke of people being beaten up, threatened and gone missing. The escalating violence came a day after security forces killed seven demonstrators in protests around the country.
In the city of Dar Saad in the southern province of Aden, medical officials said one protester was shot dead and three others wounded as police tried to disperse a demonstration. Earlier, protesters had torched three police cars and blocked roads to try to stop security troops from bringing in reinforcements.
Young activists camped out in the square continued to expand the area of their sit-in and threatened to march on the presidential palace about three miles away. Rock throwing battles between protesters and security troops broke out on the edges of the encampment.
Yemen has been hit by constant protests since mid-February. Even before that, the country's government was struggling to confront one of the world's most active al-Qaida branches, a secessionist rebellion in the south and a Shiite uprising in the north.
Yemen's demonstrators are calling for Mr Saleh to step down, a demand he has repeatedly rejected while also trying to assuage opposition groups. Mr Saleh has said he would not seek another term in office in 2013, and offered to form a national unity government with opposition figures. These overtures have failed to satisfy the protesters.