Four protesters were killed in clashes with police in southern Yemen on Thursday as unrest spread and demonstrators called for an end to President Ali Abdullah Saleh's three decades of rule.
In a seventh straight day of protests inspired by revolts in Tunisia and Egypt, 3,000 marched in the southern port of Aden and police shot in the air to disperse the crowd.
Officials at two Aden hospitals told Reuters three men died of gunshot wounds after clashes with police.
A local official earlier reported another death and said eight others had been wounded by "random gunfire".
"No to oppression, no to corruption, the people demand the fall of the regime," chanted the Aden demonstrators, gathered to protest against the killing of two men on the previous day by stray bullets as police fired in the air.
In Sanaa at least 40 were wounded as hundreds of Saleh loyalists, some armed with guns, charged around 1,500 protesters, who hurled rocks at them. Several journalists told Reuters they were beaten by loyalists, and the streets where clashes took place were stained with blood.
Late on Thursday, small-scale clashes broke out between hundreds of protesters and Saleh supporters near Sanaa university, residents said. At least one man was hurt.
Amnesty International said in a statement: "Yemenis have a legitimate right to freedom of expression and assaults against both them and journalists covering their protests are totally unacceptable."
Saleh, a U.S. ally against a resurgent wing of al Qaeda in Yemen that has launched attacks on foreign and regional targets, is struggling to quell month-old protests now erupting daily.
"We won't stop until this regime falls. We've been patient long enough," said student Salah Abdullah in Sanaa.
Around 3,000 people began their nightly rally in Taiz, where protesters have camped out in a central square for several days.
"Down with the regime, down with the oppressors, they shouted. No injuries were reported.
Young people say they are angered by corruption and soaring unemployment. A third of the Arabian Peninsula state's people face chronic hunger and 40 percent live on less than e2 a day.
The government, whose authority is weak outside Sanaa, is struggling to cement a truce with northern Shi'ite rebels and suppress an increasingly violent southern separatist movement.
Trying to calm the streets, Saleh has made concessions such as a promise to step down when his term ends in 2013 and a vow not to let his son inherit power.
The opposition coalition, which had drawn tens of thousands in rallies, has agreed to talk with him. But smaller protests have continued, organised by students and other activists using mobile text messages and Facebook.
"The protests are taking on a younger look and the inability of the opposition parties to control them is bad news for President Saleh," said Charles Dunbar of Boston University.
"The U.S. and the international community would have real cause for worry in a post-Saleh world in Yemen where the state in general and the army in particular are not in a position to maintain control should he leave."
Analysts say any uprising in Yemen, neighbour to top oil exporter Saudi Arabia, is unlikely to lead to sudden government collapse. But unrest could unfold slowly and lead to more bloodshed in a country where one in two people own a gun.
Appeal for calm
On Thursday, a state official said Yemenis were exercising their democratic rights, but warned citizens not to succumb to elements trying to create chaos, state news agencies reported.
Protests broke out in Ibb, south of Sanaa, Hodeidah in the west and Baidah in the east, each with a few hundred people.
Security forces have used force more readily in the south. The Aden municipality said it had suspended its activities in protest against the police use of violence and has promised to pay compensation for those wounded in the protests.
Saleh has toured provinces to rally support and sent his vice president to Aden on Thursday to investigate the violence.
Muslim preachers loyal to Saleh stepped into the political fray in a country where religious and tribal allegiances are often stronger than political ones. They have called for a unity government but said Saleh should stay in power.
Want to enjoy 'Zen' reading - with no ads and just the article? Subscribe todaySubscribe now