Missiles fired by Syrian warplanes hit Lebanese territory Monday, Sept 17, in one of the most serious cross-border violations since Syria's crisis began 18 months ago, AP reported citing security officials in Beirut and Lebanese state media.

The officials, speaking on condition of anonymity in line with regulations, said four missiles fired by two Syrian jets hit a rugged and remote area on the edge of the Lebanese border town of Arsal. There were no immediate reports of casualties.

Lebanon's state-run National News Agency reported that the warplanes fired three missiles that fell on the outskirts of Arsal about 500 meters (yards) from the border between the two countries.

The Syrian forces were believed to be chasing rebels in the area, which has been the site of clashes in the past between opposition fighters battling Syrian troops just on the other side of the frontier. Lebanese armed forces have in the past detained people in the region caught trying to smuggle weapons into Syria from Lebanon.

Arsal is a predominantly Sunni Muslim town, like the majority of Syria's opposition that is trying to oust President Bashar Assad from power. Assad belongs to the minority Alawite sect, an off-shoot of Shiite Islam.