Security sources said the military increased its forces in the Sunni districts that Shia protesters drive through to get to central Beirut where the Hezbollah-led opposition is holding a sit-in to topple the Western-backed government.

These districts witnessed several clashes between residents and protesters on Sunday -- from stone-throwing incidents to fights with sticks and knives.

In the most serious incident, gunmen fired from assault rifles at a group of protesters in the Sunni Qasqas neighbourhood, a stronghold for the anti-Syrian majority coalition, killing one young man and wounding others.

The opposition said the incidents would not drive it to abandon plans for toppling the government.

The Shia group Hezbollah, which is backed by Syria and Iran, and its allies in the opposition had taken to the streets and were holding an indefinite sit-in to force the resignation of Western-backed Sunni Prime Minister Fouad Siniora.

Many politicians and observers had said the crisis could spill over into sectarian strife in a country that had gone through two civil wars in the last century.

Thousands of protesters spent a third night in a newly built tent city in central Beirut outside the main government complex where Siniora was spending his days and nights.

Many banks and businesses were again closed on Monday in the downtown area, Lebanon's banking and commercial centre. Business owners in the area have said that lengthy closures could devastate several businesses and force employers to cut jobs.

The opposition, which includes some Christians, has been demanding effective veto power in the government, which has a majority comprising of anti-Syrian politicians from Christian, Sunni 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.

Arab League Secretary General Amr Moussa met Lebanese leaders in Beirut, including Hezbollah officials, to try to find a compromise, political sources said.

Moussa expressed concern at the situation and said Arab countries could not afford to be bystanders in a crisis that developed after Hezbollah's summer war with Israel.

German Foreign Minister Frank-Walter Steinmeier arrived in Syria on Monday on a brief visit to urge President Bashar al-Assad to play an active role in helping stabilize the Middle East.

Lebanon had been rocked in the past 22 months by the assassination of Hariri and five other anti-Syrian figures, the last of whom was cabinet minister Pierre Gemayel on November 21.

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