Syrian planes have bombed a Lebanese border town in eastern Bekaa Valley, the first such attack during the country’s ongoing crisis, according to a Lebanese army source.

The warplanes entered 1 kilometer into Lebanese airspace and struck the town of Kerbet Younan in the Wadi al-Khayl region of Arsal, where the majority of Sunni Muslim residents support Syrian rebels fighting to topple President Bashar al-Assad, and fired four rockets at a remote section of the border with Lebanon, according to Reuters.

Conflicting reports have emerged over whether Lebanese territory was hit in the airstrike.



"Syrian planes bombed the border between Lebanon and Syria but I cannot yet say if they hit Lebanese territory or only Syrian territory," Lebanese news website Naharnet quoted a military official, speaking on condition of anonymity.



The mountainous desert region of Arsal is said to be ideal terrain for the smuggling of arms and the flow of fighters across the border. The Syrian warplanes targeted two barns used by "armed men," Al-Manar reported.

One of the local residents told AFP that the missiles had fallen in an agricultural area.



No injuries were reported.

An army patrol has been dispatched to the border region to determine whether the Syrian missile hit Lebanese territory, or the two countries’ shared border, Naharnet said.

The US State Department later confirmed that Syrian government aircraft fired rockets into northern Lebanon and it described the incident as "a significant escalation."



"This constitutes a significant escalation in the violations of Lebanese sovereignty that the Syrian regime has been guilty of. These kinds of violations of sovereignty are absolutely unacceptable," State Department spokeswoman Victoria Nuland told reporters.



The airstrike comes less than a week after Syria threatened to attack Lebanese territory if "terrorist gangs" continue to infiltrate the country. On Thursday, Syria submitted a letter of protest to Lebanese authorities, complaining of “violations of the neighboring country's territory on the border."

Lebanon publicly vowed it would not become involved in the Syria conflict. However, officials believe Lebanon remains at risk of being dragged into the two-year long war, which according to UN estimates has killed more than 70,000 people.

