Dubai: Syria's violence has spilled into neighbouring Lebanon where four people were killed in fierce fighting between supporters and opponents of President Bashar Al Assad, reports said.

Rocket-propelled grenades and automatic rifles were used in the fighting in an Alawite enclave and surrounding Sunni neighbourhoods in the port city of Tripoli, 70km north of Beirut. Al Assad is a member of the Alawite sect, a Shiite offshoot.

The violence was sparked when Lebanese authorities detained a Sunni cleric, Shaikh Shadi Al Mawlawi, according to local media reports. His followers accused the government of arresting Al Mawlawi because he was helping Syrian refugees in Tripoli, while authorities said he is under investigation for his alleged ties to a terrorist organisation.

A statement from the Lebanese army said reinforcements were being sent to the city and that troops were "pursuing armed men to return the situation to normality." A Reuters correspondent in the city said most of Tripoli's main intersections were blocked by burnt tyres and that the Lebanese army had deployed in an area separating the Alawite enclave from the rest of the city.