There have been fierce clashes in eastern Lebanon between Sunni militants and Lebanese Shia group Hezbollah.
The Sunni militants are believed to be from al-Qaeda’s Syrian affiliate, the al-Nusra Front.
Hezbollah officials have said at least two of its fighters, and at least 16 Nusra fighters, were killed.
The clashes erupted after gunmen attacked Hezbollah bases over a wide area from south of the town of Baalbek, north to near the border town of Arsal.
Lebanon’s official National News Agency also reported the clashes, saying they began after an attack launched by gunmen from Asaal al-Ward in Syria’s Qalamoun province.
Hezbollah’s al-Manar television reported late on Sunday that the group had pushed the insurgents back over the border and the clashes had ended.
Lebanon’s border with Syria is porous and largely unpatrolled.
Hezbollah maintains several military posts along inaccessible parts of the border but rarely gives details on clashes with other fighters.
The clashes come two months after al-Nusra and IS militants attacked Lebanese security forces in the border town of Arsal, capturing several personnel as hostages. They have since executed at least three of them.
Hezbollah fighters have previously fought alongside government troops in Syria, against rebels supported by many Syrian Sunnis.
The conflict in Syria has exacerbated existing tensions in Lebanon, and made Hezbollah and areas which support it targets for Sunni militant bomb attacks.