Beirut : Tens of thousands of pro-Syrian protesters continued a sit-in aimed at ousting Lebanon's government yesterday as the country's political crisis showed no sign of easing.

Hezbollah and its allies in the opposition, including some Christians, held a third day of protests at a tent city in central Beirut, within earshot of the office-turned-residence of Prime Minister Fouad Siniora.

"Our one and only demand is a government of national unity," senior pro-Syrian Christian opposition figure Suleiman Franjieh told a jubilant crowd massed at Beirut's Riad Al Solh square.

"We will stay in this square ... we will not leave until this illegal and unconstitutional government goes."

Arab League secretary-general Amr Mousa described Lebanon's political crisis as "serious" upon his arrival in Beirut yesterday for talks with the deadlocked parties.

Lebanon's Western-backed government has pledged not to give in to demands by the Shiite Hezbollah-led opposition to resign.

"The situation in Lebanon is serious and all we can do is watch and observe," the head of the 22-member Cairo-based Arab League said.

Following talks with Siniora, Mousa spoke to reporters again, saying: "We are aware of the dangers and we hope that it won't escalate.

"Our job is to work with all parties on the basis of achieving national unity. We are concerned about Lebanon," he added.

Although the dispute started out over political differences, it is moving closer to a sectarian crisis as tension between Sunni and Shiites is high and there is ill feeling among Christians who are divided between the rival camps. In a sign the protests could disintegrate into violence, a van carrying protesters was stoned as it drove through the Sunni QasQas neighbourhood of Beirut, security sources said.

The army broke up the crowd, but not before the passengers left the vehicle and chased some stone throwers, smashing a few cars. Four passengers were injured.

Government supporters, who held their own mass funeral procession for an assassinated anti-Syrian cabinet minister 12 days ago, stayed away from central Beirut, heeding calls by leaders to avoid street confrontations.

"We will be steadfast, peacefully and democratically. We are here and when they are convinced that there is no solution except through dialogue, then welcome," said anti-Syrian Druze leader Walid Junblatt.

Despite the city centre's paralysed streets, a previously scheduled Beirut Marathon, held under the motto 'For the Love of Lebanon', went ahead with runners using suburban roads to skirt the demonstration. The opposition led by Hezbollah, which is backed by Syria and Iran, has been demanding effective veto power in the government, whose majority comprises anti-Syrian politicians from Christian, Sunni and Druze parties.