Unrest in Yemen turned ugly as protesters clashed with police and government loyalists in Sanaa on the fourth consecutive day of rallies.
Thousands of protesters demanding the resignation of President Ali Abdullah Saleh came up against a smaller crowd backing the veteran leader.
The protesters could be heard chanting "After Mubarak, Ali", in reference to the recent dramatic events in Egypt.
Police fired tear gas and stones were thrown, with reports of injuries.
Clashes also broke out during an anti-government protest in the Yemeni city of Taez, to the south of the capital.
The Middle East has seen a wave of anti-government protest this year, which began with the overthrow of Tunisia's President, Zine al-Abidine Ben Ali, last month and reached a new height at the weekend, when Hosni Mubarak of Egypt resigned.
On Monday, violence erupted at an opposition rally in the Iranian capital Tehran, while in Bahrain, security forces fired tear gas and rubber bullets to disperse dozens of protesters in the capital, Manama.
In the Manama violence, there were reports of at least one death and some 20 people injured.
Beaten by police
Yemeni protesters marched towards Tahrir (English: liberation) Square - which bears the same as Cairo's main square - to demand an end to President Saleh's 32-year rule.
An AFP news agency report put their number at 3,000, which would be 1,000 more than during Sunday's protest in the city.
As the protesters approached the square, riot police moved in and clashes broke out, eyewitnesses said.
Government loyalists armed with broken bottles, daggers and stones chased the protesters, Reuters news agency reports.
BBC correspondent Abdullah Gorab and his cameraman were beaten and injured by police.
Mr Gorab described what happened, telling the BBC: "I am now escaping from the police.
"I'm bleeding from my head. The policemen who were accompanying a prominent official figure, Hafez Meayad, were running after me after they asked more than 50 protesters from the ruling party to hit us.
"They took my phone and the cameraman's phone. They beat any correspondent who tries to film the attack on the protesters. This is the current regime now in Yemen. No rule, no law. I'm bleeding now as I escape from the police."
Police locked several thousand protesters inside the local university to minimise bloodshed, the agency says.
It was unclear how many people were injured in Sanaa. In the unrest in Taez, at least eight people were hurt.
Mr Saleh is reportedly preparing to hold talks with opposition groups on possible political reforms, in an attempt to prevent his overthrow in the manner of Egypt and Tunisia.
He has promised he will stand down in 2013 and that his son will not replace him in office.
Yemen, the poorest country in the Arab world, is a key ally for the US in its efforts to combat al-Qaeda in the region.
The country also faces a separatist movement in the south and an uprising of Shia rebels in the north.