The Lebanese authorities have increased the army and police presence in Beirut as protests against the Western-backed government continue into a fourth day.
Troops are on guard to stop political friction becoming sectarian strife
A protester was shot dead on Sunday - the first casualty since militant group Hezbollah called for the protests.
Ahmed Mahmoud, a Shia, was killed by an unknown gunman in a Sunni district, but details of the incident are unclear.
A BBC correspondent says the situation in the city remains very tense, with streets to Sunni areas closed off.
Sunni Muslim districts were the scene of several clashes between residents and protesters on Sunday, with some adversaries wielding sticks and knives.
The deadly shooting incident happened in the Qasqas neighbourhood.
Observers say such incidents could provoke widespread inter-communal strife in a country that was brought to its knees by civil war in the 1970s and 1980s.
The head of the Arab League, Amr Musa, is visiting Beirut to offer to mediate between the government and the opposition, and envoys from the United Arab Emirates, Bahrain and Tunisia are offering their help.
Thousands of pro-Syrian protesters have spent three nights in a tent city in central Beirut outside the government office of anti-Syrian Prime Minister Fouad Siniora.
They accuse Mr Siniora of being too pro-Western and anti-Syrian, and of failing the Lebanese people.
The opposition, led by the Shia Muslim militant and political movement Hezbollah with some prominent Christian allies, has been demanding an effective veto power in the government.
The current crisis was sparked last month when five Shia ministers and one Christian minister quit the government.
Hezbollah had asked for cabinet seats that would give it and its allies power of veto, but the majority group in parliament refused.
The political tension was increased two weeks later with the assassination of a leading anti-Syrian minister, Pierre Gemayel.
The government came to office last year in the first election after the withdrawal of Syrian troops, originally stationed in Lebanon during the civil war.
Syria was forced to withdraw its forces after massive protests and international pressure, triggered by the February 2005 assassination of former Lebanese Prime Minister Rafik Hariri.