Missiles fired by Syrian warplanes hit Lebanese territory on Monday in one of the most serious cross-border violations since Syria’s crisis began 18 months ago, security officials in Beirut and Lebanese state media said.

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.

“I heard several explosions and saw four clouds of dust billowing from the area,” Arsal resident Nayeh Izzedine said by telephone referring to the border. “I don’t know if it was an air raid but there was a plane in the sky.”

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.

Syrian shells have hit Lebanese territory in the past but the air raid appears to be the most serious violation. Several Lebanese, including a journalist, have been killed and dozens wounded by fire coming from the Syrian side.

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