BEIRUT: At least 12 Syrian rebels were killed overnight in east Lebanon in an ambush by Hezbollah, security sources said, adding that one member of the resistance group was also killed, in the first confrontation between the rivals on Lebanese soil.

The sources, who spoke on condition of anonymity, said the deadly clash between the two sides took place in Ain al-Jawzeh, 3 kilometers east of Baalbek.

They said the area has been frequently used by rebels as a site for launching rocket attacks.

Media reports varied on the number of fighters killed in the incident.

AlMayadeen TV said 17 members of the Syria’s Nusra Front were killed in the clashes, adding that the rebels had been preparing rocket launchers at the time.

Lebanon’s LBCI television said 14 members of the Free Syrian Army had been killed in the clashes, with only one fatality from the ranks of Hezbollah. It said four members of the Lebanese resistance group were also wounded.

Sunday morning saw heightened activity by Israel’s air force over east Lebanon, with low-altitude flights spotted over Baalbek. The National News Agency said warplanes also flew over the eastern Bekaa Valley, south Lebanon and the Lebanese capital.

The overnight fighting in the district of Baalbek comes after Syrian rebels threatened Hezbollah last week they would target the Lebanese group over its military involvement in Syria.

Syrian government forces backed by Hezbollah have been waging battles since May 19 against the Syrian rebel-held town of Qusair, which lies near the border with Lebanon.

Lebanon has seen a rise in the number of security incidents linked to the crisis in Syria, including a renewed round of clashes between supporters and opponents of Syrian President Bashar Assad in the north of the country and almost daily rocket attacks from the Syrian side of the border.

On Saturday, over a dozen rockets from Syria fell in different parts of east Lebanon.

Three Syrian rockets also hit the Bekaa Valley city of Hermel Sunday morning, leaving no casualties, a security source told The Daily Star.

In a fiery speech last month, Hezbollah chief Sayyed Hasan Nasrallah urged that the fighting remain restricted to the confines of Syria.

“We [Hezbollah] are fighting in Syria, you are fighting in Syria, let us continue to fight there,” he said. “Put Lebanon aside.”