On Monday missiles fired by Syrian warplanes hit Lebanese territory, according to the Associated Press.
Security officials in Beirut told state media that the strike was one of the most serious cross-border violations since the Syrian crisis began.
The officials, who all spoke on condition of anonymity, told the AP that four missiles fired by two Syrian jets hit a remote area on the edge of the Lebanese border town of Arsal.
Arsal resident Nayeh Izzedine further told the AP, "I heard several explosions and saw four clouds of dust billowing from the area. 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.
According to the Financial Times, this is not the first time that Syrian forces have fired shells into Lebanon. In July, foreign minister Adnan Mansour sent a letter asking Syria to refrain from troop incursions.
The Financial Times also noted that Arsal is a city comprised of mostly Sunni residents. The town has reportedly seen a huge influx of refugees attempting to escape the fighting in Syria.
According to a recent UN report, it is air strikes like the one on Lebanese soil that are causing the majority of civilian causalities in the Syrian conflict. The report added that both government and anti-government forces committed war crimes and crimes against humanity.
Paulo Pinheiro, the Brazilian investigator leading a United Nations commission of inquiry, told the UN Human Rights Council that the inquiry has compiled enough evidence, including names of possible war criminals, to "support future action by national or international courts," according to the New York Times.
For complete coverage of the Syrian conflict visit our Inside Syria series.