Thousands of Yemenis took to the streets of three provinces for a second successive day on Sunday to demand the independence of the country's south, witnesses said.

The protests in Abyan, Daleh and Lahj provinces were conducted in tandem with a two-day international donors' meeting in Saudi Arabia on aiding the country.

"Thousands of men and women went out in Lahj province carrying pictures of former Vice President Ali Salem Al-Bidh and southern flags," a witness said.

Bidh, who led the south to unity with the north in 1990 but is now a major separatist leader, had called on Friday for "two days of southern anger" to coincide with the donors' meeting.

Witnesses said the protests on Sunday were peaceful, without any major confrontations with security forces, which are heavily deployed across the south.

But police fired tear gas to disperse demonstrators in the city of Daleh, witnesses said.

Three Abyan civilians suffered bullet wounds on Saturday when police moved to stop protesters cutting the highway between the provincial capital Zinjibar and the south's main city Aden, witnesses said.

General Ghazi Ali Mohsen, head of security in Daleh province, said 21 "rioters" were arrested in Daleh.

"The subversive elements were carrying weapons and flags and calling" for the secession of the south from the north, Mohsen said.

Yemen, the poorest Arab country, struck a truce on Feb. 11 with rebels who have been fighting over religious, economic, and social grievances in the north.

On Saturday it imposed tougher security measures in Dalea, where separatist tensions have been rising. These included a ban on carrying weapons in public, two days after a policeman was shot dead in an ambush in a nearby province.

The policeman's death on Thursday brought to four the number of people killed in attacks on security personnel in the south in a week as authorities mounted arrest sweeps targeting separatists.

People in the south, home to most Yemeni oil facilities, complain that northerners have abused the 1990 agreement uniting the country to grab resources and discriminate against them.