Fighting flares in Lebanese city over Syria loyalties TRIPOLI, Lebanon (Reuters) - Four people were killed and 15 wounded in overnight gun battles in the Lebanese city of Tripoli in a second night of fighting between Sunni and Alawite gunmen loyal to different sides in the war in neighboring Syria, a military source said on Tuesday. In the capital Beirut, tension eased after troops fanned out across the city to clear the streets of gunmen who had clashed on Sunday night. The violence flared after the assassination of senior Lebanese security official Wissam al-Hassan, who was opposed to the Syrian leadership, in central Beirut on Friday. The bombing and the ensuing clashes brought the civil war in Syria into the heart of Lebanon and triggered a political crisis, with the opposition demanding the resignation of the mostly pro-Damascus cabinet of Prime Minister Najib Mikati. The fighting in Tripoli took place between the neighboring areas of Bab al-Tabbaneh, a Sunni Muslim stronghold, and Jebel Mohsen, an Alawite district. Three Sunnis and one Alawite were killed and 15 people were wounded, a military medical source told Reuters. Residents said combatants traded machinegun-fire and rocket-propelled grenades. On Tuesday morning, Tripoli's center was busy and traffic moved freely. Lebanese army soldiers kept watch in armored vehicles mounted with heavy machine guns. But shops close to the combat zone were shuttered. A fruit market on the front line was closed and residents said they feared snipers. Teenagers in t-shirts with guns hid behind buildings to peek out up the hill into Jebel Mohsen. Tripoli's Sunni Muslims support the Syrian rebels fighting to overthrow President Bashar al-Assad, who are mostly from Syria's Sunni majority. Assad is a member of the Alawite sect, an offshoot of Shi'ite Islam. He can count on the support of Hezbollah, a powerful Shi'ite Islamist armed group that is part of the Mikati government, as well as other Shi'ites and Alawites in Lebanon's complex sectarian and political mix. The overnight violence in Tripoli - which has suffered previous bouts of fighting since the Syrian conflict started 19 months ago - brought the toll to at least 10 dead and 65 wounded since Friday. Lebanon is still haunted by its 1975-1990 civil war, which made Beirut a byword for carnage and wrecked large parts of the city. Many Lebanese fear the Syrian war will propel their country back to those days, destroying their efforts to rebuild it as a center of trade, finance and tourism with a measure of democracy. Opposition politicians have accused Syria of being behind Friday's killing of Brigadier General Hassan, who had worked to counter Syrian influence in Lebanon. A Sunni Muslim, he helped to uncover a bomb plot that led to the arrest and indictment in August of a pro-Assad former Lebanese minister. He also led an investigation that implicated Syria and Hezbollah in the 2005 assassination of Rafik al-Hariri, a former prime minister of Lebanon. Mikati, who is also a Sunni Muslim, had personal ties to the Assad family before he became prime minister in January last year. His cabinet includes Hezbollah as well as Christian and other Shi'ite politicians close to Damascus. He offered to resign at the weekend to make way for a government of national unity but President Michel Suleiman persuaded him to stay in office to allow time for talks on a way out of the political crisis. If he were to stand down before an alternative was worked out, it would mean the collapse of the political compromise that has kept the peace in Lebanon. Free Patriotic Movement parliamentarian Michel Aoun, a Christian politician and an ally of Hezbollah, said Lebanon could not live with such a power vacuum, and noted that formation of a government could take six months or more. "What happened (Hassan's assassination) constitutes a security setback but if there was a vacuum, maybe the country would be in chaos," he told the Beirut Daily Star newspaper. Writing by Angus MacSwan; Editing by Kevin Liffey