The Beirut street battles overnight killed at least two people and wounded 15, and were the most serious clashes in the capital in four years. The streets were calmer by Monday morning but some shops remained closed and many parents kept children home from school.
The violence in Beirut's predominantly Sunni neighborhood of Tariq Jadidah erupted hours after Sheik Ahmed Abdul-Wahid and his bodyguard were shot dead at a checkpoint in northern Lebanon. Abdul-Wahid was an anti-Syrian cleric.
Authorities braced for the possibility of more violence Monday in the north, where Abdul-Wahid was to be buried. Gunmen carrying automatic rifles shouted for the downfall of the Syrian regime in the cleric's hometown of Bireh.
The fighting underscores how the bloodshed in Syria, where President Bashar Assad's regime is cracking down on an uprising against his rule, can fuel violence across the border in Lebanon.
Lebanon has a fragile political faultline precisely over the issue of Syria.
There is an array of die-hard pro-Syrian Lebanese parties and politicians, as well as support for the regime on the street level. There is an equally deep hatred of Assad among other Lebanese who fear Damascus is still calling the shots here. The two sides are the legacy of Syria's virtual rule over Lebanon from 1976 to 2005 and its continued influence since.
Thousands poured into a square outside a mosque in Bireh to take part in the funeral. The cleric's coffin, which was brought to his home, was covered with a Lebanese flag and a flag used by Syrian rebels.
"Oh cleric, we want revenge against Nasrallah and Bashar," screamed the men who carried the coffin. The leader of Lebanon's Hezbollah militant group, Sheik Hassan Nasrallah, is a strong ally of Syria.
Earlier, gunmen shouted "Down with Bashar!" and said the Syrian leader was trying to "transfer the crisis to Lebanon." Scores of men opened fire with their rifles in the air as a sign of mourning.
Most businesses and schools were closed in the predominantly Sunni northern Lebanon after local officials called for a general strike to protest the cleric's killing.
The circumstances surrounding Sunday's shooting death of the Abdul-Wahid remained unclear but the state-run National News Agency said the cleric and his bodyguard appeared to have been killed by soldiers after their convoy failed to stop at an army checkpoint.
The Lebanese army on Sunday issued a statement, saying it deeply regretted the incident and that a committee will investigate.
Amid fears the situation might deteriorate, four Gulf countries - Kuwait, Qatar, Bahrain and United Arab Emirates - have warned their citizens against travel to Lebanon.
Lebanon and Syria share a complex web of political and sectarian ties and rivalries, which can easily turn violent. Last week, clashes sparked by the Syrian crisis killed at least eight people and wounded dozens in the northern city of Tripoli.
The revolt in Syria began 15 months ago, and there are fears the unrest will lead to a regional conflagration that could draw in neighboring countries. The U.N. estimates the conflict has killed more than 9,000 people since March 2011.
Syrian activists said regime forces killed dozens of people during a raid Sunday on the central town of Soran in Hama province, security officials said.
One activist group, the Britain-based Syrian Observatory for Human Rights, put the death toll at 39, citing a network of sources on the ground. Syria-based activist Mustafa Osso said the figure was more than 20.
The death toll could not be independently confirmed. Syria's state media reported that four soldiers were killed Sunday in the Hama province during clashes with gunmen.
A video posted online by activists showed the bodies of five people said to be of the same family who were killed during the shelling of Soran.
Syria is a geographical linchpin in the Middle East, raising the possibility that the crisis there will bleed into other countries.
The clashes in Beirut subsided around 4 a.m. Monday after anti-Syrian gunmen took control of the headquarters of the pro-Syrian Arab Movement Party.
The fighting was among the most intense fighting in Beirut since May 2008, when gunmen from the Shiite Hezbollah militant group swept through Sunni neighborhoods after the pro-Western government tried to dismantle the group's telecommunications network. At the time, more than 80 people were killed in the violence, pushing Lebanon to the brink of civil war.
Also Monday, Syria's state-run news agency SANA, said Assad issued a presidential decree calling on the country's newly elected parliament to hold its first meeting on Thursday. A parliament speaker is usually elected on the first meeting of a new parliament.
Assad has pointed to the parliamentary elections earlier this month as a sign of his long-promised reforms, but the opposition dismissed the vote as a sham meant to preserve his autocratic rule.
As the violence intensified, there are growing fears that al-Qaida or other extremists could be entering the fray. In a statement posted on a militant web site late Sunday, a group calling itself the Al-Nusra Front claimed responsibility for a suicide car bomb attack in the parking lot of a Syrian military compound in the eastern city of Deir el-Zour.
Saturday's attack, the latest in increasingly frequent bombings in major Syrian cities to target the regime's security services, killed at least nine people and wounded dozens.
Little is known about the group although Western intelligence officials say it could be a front for a branch of al-Qaida militants from Iraq operating in Syria. The group claimed responsibility for several other suicide attacks in Syria.