Sanaa/Aden: Tens of thousands of protesters demanding the end of President Ali Abdullah Saleh’s 32-year rule of Yemen joined demonstrations on Monday, while skirmishes in the south killed three soldiers and a policeman.

Witnesses said around 5,000 protesters who have camped out nightly in the streets near Sanaa University, shouted “We have one demand: the fall of the oppressor."

Protests against Saleh, a US ally against an al Qaeda wing based in Yemen, have spread across the impoverished Arabian Peninsula state in more than a month of protests.

“Leave and take your corruption with you," the protesters in Sanaa shouted.

In the northern cities of Ibb and Hudeida, thousands of protesters gathered while at least 10,000 took to the streets in Taiz, 125 miles south of the capital.

Opposition to Saleh, who was previously confronting an on-off Shi’ite Muslim revolt in the north and a secessionist insurgency in the south, has now spread across the country, galvanised by successful uprisings in Egypt and Tunisia.

Yemen is already teetering on the brink of state failure. One in two people own guns, 40% of the population lives on less than $2 a day and a third face chronic hunger.

Violence against security forces has spiked in recent days, though it is unclear who has been behind the attacks.

A local official said two soldiers were killed and 11 wounded on Monday in two attacks by armed men in Makhzan in the flashpoint Abyan province. The gunmen attacked a security checkpoint, killing a soldier and wounding seven, he said.

A second attack on a car carrying the wounded away killed another soldier and wounded four. The official blamed al Qaeda.

In the province of Hadramout, an official said the head of a local intelligence branch was shot dead on Saturday by men on motorcycles who sped off after the attack.

In further unrest, prison riots broke out in the southern province of Mahra, near the border with Oman on Sunday. One inmate was killed in clashes with police. Four prisoners escaped. Two guards suffered burns.

Islamists, tribesmen join protest

The protests that have gained steam under student and activist leadership in recent weeks were swelled on Monday by members of several tribes, which are at the heart of Yemen’s social system. Islamist groups also joined the sit-in.

The protesters formed separate groups around the campus, with some waving Yemen’s white, red and black striped flags while others sang and danced, witnesses said.

The daily protests in Yemen had already drawn in separatists and opposition parties which have returned to the streets after dropping earlier plans for dialogue with the 68-year-old Saleh.

Saleh, apparently trying to bolster military support, met armed forces commanders at the weekend, and told them they were responsible for maintaining security and stability in the face of a plot against Yemeni unity, Saba state news agency said.

“We are confident that our people and the great national institutions will abort any plots," Saleh was quoted as saying.

“We say to the Yemeni people that the homeland is in safety as long as it is in the hands of their brave sons, who will defend their unity," the president added.

Violence between pro- and anti-government demonstrators, once common, has calmed down since Saleh asked police to protect protesters and prevent clashes between rival factions.

But protests have been more violent in the once-independent south. Twenty-four people have been killed in daily demonstrations across Yemen in the past two weeks.