Militants supporting opposing sides of Syria's civil war clashed in the southern Lebanese city of Sidon on Tuesday, June 18 killing one, a security source said, rocking a city where divisions have been simmering for months, according to Reuters.

Syria's war started with pro-democracy rallies but was suppressed by forces loyal to President Bashar al-Assad. Now majority Sunni Muslim rebels wage war against his armed forces, which are led by Alawites, an offshoot of Shi'ite Islam.

In Sidon, supporters of ultra-conservative Sunni cleric Ahmad al-Assir shot machineguns and rocket-propelled grenades at the neighborhood of Abra, which is home to armed supporters of the Shi'ite militant group Hezbollah, an organization fighting for Assad in Syria, the source said.

He added that Assir's men started the clashes after one of their supporters was attacked in his car by men from Abra.

"A man was killed inside his shop by Assir's men," the security source said on condition of anonymity.

A source at a hospital in Sidon said that an elderly man was killed and four were wounded, including two fighters. It was not clear if the elderly man was the same person as the man killed in his shop.

Dozens have been killed in Syria-related clashes in Lebanon's northern city of Tripoli during the 27-month-old conflict in Syria, which has killed 93,000 people, according to the United Nations.

Sidon has seen sporadic violence but on Tuesday the army blocked several roads and resident said that many streets were full of armed men.

Half a million Syrian refugees have fled to Lebanon, which suffered its own 15-year civil war that ended in 1990 and is struggling to cope with the influx of mostly Sunni Syrians.