Protesters demand the release of rights activists detained during recent demonstrations in Sanaa. (Khaled Abdullah/Reuters)

Tens of thousands of Yemenis demanded the president step down in nationwide protests Thursday, taking inspiration from the popular revolt in Tunisia and vowing to continue until their U.S.-backed government falls.

Yemen is the latest Arab state to be hit by mass anti-government protests, joining Tunisia and Egypt in calls for revolutionary change. The demonstrations pose a new threat to the stability of Yemen, the Arab world's most impoverished nation, which has become a haven for al-Qaeda militants.

"No delays, no delays, the time for departure has come!" shouted protesters, calling for the ouster of President Ali Abdullah Saleh, who has ruled for nearly 32 years. Saleh's government is riddled with corruption, has little control outside the capital, and its main source of income — oil — could run dry in a decade.

The protesters were led by opposition members and youth activists in four parts of the capital, Sanaa. In the southern provinces of Dali and Shabwa, riot police used batons to disperse people, while thousands took to the streets in al-Hudaydah province, an al-Qaeda stronghold along the Red Sea coast.

Self-immolation in Aden

In the southern port city of Aden, a 28-year-old unemployed man set himself on fire to protest the economic troubles in the country. The man, identified as Fouad Sabri, was rushed to the hospital in critical condition, medical officials said. The act is the latest in a wave of attempts at self-immolation across the Arab world, which appear to be inspired by events in Tunisia.

A few hundred pro-government supporters held a counter-protest in Sanaa, but they were greatly outnumbered. There were no immediate reports of violence or major unrest in the capital.

The protests calmed by early evening, but organizers said there was more to come Friday.

Hakim Almasmari, editor in chief of the Yemen Post, said that the protests are the largest in over a decade.

"We estimate at least a hundred thousand protesters, even though the government is trying to make media announce less than that," he said.

"This really shows that the opposition parties are very serious about going against the president.… All chances of having dialogue with the ruling party are vanishing."

Concessions made by president

Saleh has tried to defuse simmering tensions by raising salaries for the army and by denying opponents' claims he plans to install his son as his successor.

After the Tunisian revolt, which forced that country's president to flee into exile, Saleh ordered income taxes slashed in half and instructed his government to control prices. He deployed anti-riot police and soldiers to several key areas in the capital and its surroundings to prevent riots.

That hasn't stopped critics of his rule from taking to the streets in days of protests calling for Saleh to step down, a line that few dissenters had previously dared to cross.

"We will not accept anything less than the president leaving," said independent parliamentarian Ahmed Hashid. "We'll only be happy when we hear the words 'I understand you' from the president," invoking a statement issued by Tunisian President Zine El Abidine Ben Ali before he fled the country.

Nearly half of Yemen's population lives below the poverty line of $2 a day and doesn't have access to proper sanitation. Less than a tenth of the roads are paved. Tens of thousands have been displaced from their homes by conflict, flooding the cities.

The country is enduring a rebellion in the north and a secessionist movement in the south.

Saleh's current term in office expires in 2013 but proposed amendments to the constitution could let him remain in power for two additional terms of 10 years.

With files from CBC News