BEIRUT, Lebanon (Reuters) -- Lebanon's political crisis showed no sign of easing on Sunday, as thousands of pro-Syrian protesters pressed on with a sit-in aimed at ousting a Western-backed government intent on holding on to power.

The Shiite Muslim group 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.

"We are not letting them (ministers) sleep, we're disturbing them with our noise. We have the resilience to stay not for one month, but a year or two," said Ahmed Kayello, 20, from south Lebanon, sitting on a grassy slope.

A sea of orange, the color of Christian opposition leader Michel Aoun's movement, gathered in front of the St. George Cathedral in the city center, where a Maronite Christian priest conducted Sunday mass.

Arab League Secretary General Amr Moussa arrived in Beirut to meet Lebanese officials, expressing concern and saying Arab countries could not afford to be bystanders in a crisis that developed after Hezbollah's summer war with Israel. "The stability of Lebanon and moving towards a solution that would bring about a sure future for the country is one of our concerns," he said.

"All of us are worried about the situation in Lebanon."

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 Jumblatt.

Despite the city center's paralyzed 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.

Veto power

The opposition led by Hezbollah has been demanding effective veto power in the government, whose majority comprises anti-Syrian politicians from Christian, Sunni Muslim and Druze parties.

But these politicians say the opposition only wants to weaken the government and derail a UN tribunal that would try suspects in the 2005 murder of ex-premier Rafik al-Hariri.

A preliminary UN inquiry has implicated Syrian and Lebanese security officials in the killing, which led to Syrian forces being forced to withdraw from Lebanon last year.

Six opposition ministers resigned from the cabinet last month after talks on national unity collapsed. But the depleted government approved plans for the tribunal, sparking the latest protests.

The cabinet was also weakened by the November 21 assassination of anti-Syrian minister Pierre Gemayel. A memorial mass for Gemayel took place at the Governmental Palace on Sunday, attended by Siniora and other anti-Syrian politicians.

Siniora, who has vowed he will not be forced out by the protests, has won expressions of support from Arab and Western governments, including the United States, Britain and Germany.

Political sources from both camps said there were no serious moves to end the deadlock. "We don't expect the showdown to be resolved any time soon," one source said on Saturday.

Although the dispute is political, many Lebanese fear sectarian violence could erupt. Tension between Sunni and Shiite Muslims is high and there is ill feeling among Christians who are divided between the rival camps.

Hezbollah has repeatedly criticized Siniora's government over what it says was its failure to back the group during its 34-day conflict with Israel.