Police who had been trying to keep the sides apart locked several thousand fleeing protesters inside the Sanaa University campus near where they were rallying to stem the bloodshed.

Five people were wounded in the melee, an opposition source said, and a BBC photographer said he was badly beaten by police.

“Hey Ali, get out, get out!” protesters shouted, referring to President Ali Abdullah Saleh, a US ally against Al-Qaeda’s resurgent Yemen-based wing in power for over 30 years.

Protests in impoverished Yemen have gained momentum in recent weeks, sometimes drawing tens of thousands of people, but have become more and more violent since Friday with clashes between rival protesters and police or pro-government groups.

The threat of turmoil in Yemen, already teetering on the brink of failed statehood, has pushed Saleh to offer significant concessions, including a pledge to step down in 2013 and an invitation to the opposition for a reconciliation dialogue.

Analysts doubt Yemen will see a quick, Egypt-style revolt. Any upheaval would likely unfold slowly and perhaps with more bloodshed in a heavily armed country where tribal allegiances run strong. But the recent protests may signal a turning point.

“Yemen, and particularly President Saleh, is entering a very critical several weeks,” said Gregory Johnsen, a Yemen analyst at Princeton University, who said the resignation of Egypt’s President and the emergence of unplanned protests outside the formal opposition coalition signalled a “crisis point.”

The Egypt solidarity rallies that have morphed over the last four days into spontaneous anti-Saleh protests have been confronted by Saleh backers that Human Rights Watch says are “pro-government thugs.”

“With our blood and soul, we sacrifice for you Ali!” the armed men chanted before violence erupted.
 

Another 12 people were hurt south of Sanaa, where police fired shots in the air as hundreds of anti-government demonstrators clashed with Saleh supporters, according to witnesses in agro-industrial Taiz, where thousands of protesters held a night-long rally.

The disturbances occurred while Saleh and the main opposition group were preparing for talks that the government hoped would help avert an Egypt-style revolt. They were due to begin within days, an opposition official has said.

Saleh, under pressure from Washington to make good on promised reforms, postponed a US visit scheduled for later in the month due to regional conditions, a state news agency said.

Human Rights Watch criticized Yemeni police for what they described as unnecessary brutality against demonstrators, including the use of electroshock tasers.

“Without provocation, government security forces brutally beat and tasered peaceful demonstrators on the streets of Sanaa,” said Sarah Leah Whitson, the Middle East and North Africa director of the US-based rights group.

Police crackdowns have been harsher in Taiz than in Sanaal. But security forces have beaten detained journalists and broke up a march on the presidential palace on Sunday with batons, witnesses said. Protesters then hurled rocks at police.

Even as it faces popular unrest and is fighting Al-Qaeda militants, Yemen is also struggling to quell a separatist rebellion in the south and cement a cease-fire with Shiite Muslim insurgents in the north.