Gunmen on Saturday encircled several Lebanese army checkpoints near Arsal on the border with Syria after troops detained a suspected member of a Syrian jihadist rebel group, security sources said.
The standoff close to the town, many of whose residents support the uprising against Syria's President Bashar al-Assad, came after the arrest at a checkpoint.
"Armed groups surrounded army checkpoints in the Arsal area after the detention of Syrian Imad Ahmed Jomaa who is linked to Al-Nusra Front," a security source said.
He did not specify how many army checkpoints had been surrounded or identify the gunmen.
In a statement, the army said it had arrested Jomaa at noon and that he had admitted to belonging to Al-Nusra Front, which is Al-Qaeda's Syrian affiliate.
A local official told AFP that the situation in the area was "tense" and the security source said the army was "ready for all eventualities," including possible attacks on the checkpoints.
Arsal is a predominantly Sunni town hosting tens of thousands of Syrian refugees and has supported the Sunni-led uprising against Assad.
The area has been the scene of frequent tensions with Lebanese security forces, as well as air raids and shelling by Syrian troops across the border who say they are targeting rebel forces holed up in the mountainous region.
Al-Nusra Front has been fighting against Syrian government forces along with other rebel groups.
It has also fought against the Islamic State (IS), a radical jihadist group which has declared a "caliphate" in territory it has seized straddling Syria and Iraq.
Despite the conflict between the two jihadist groups, they have also fought alongside each other in some areas of Syria, including the Qalamun region which borders Lebanon.
A monitoring group said at least 50 members of Al-Nusra and the IS were killed in fighting in the area late Friday against regime troops and their allies from Lebanon's Shiite movement Hezbollah.