Syria's air force launched two strikes on the outskirts of Lebanon's frontier town of Arsal on Monday, causing no casualties, a Lebanese security source said.
The raid was the latest in a string of cross-border strikes against Arsal. On January 17, shells rained down on the town, killing eight people, including five children.
A December air raid prompted the Lebanese army to fire back with anti-aircraft guns.
Arsal's residents support the revolt against President Bashar al-Assad, and the town has become home to thousands of Syrians who have fled the conflict.
In a separate development, the Lebanese army said it has detained two Syrian men, including Radwan Mahmud Ayyush, a defector from Syria's army, in the Wadi Hmeid area of Arsal.
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"As part of operations to bring the land borders under control, army units in the area of Wadi Hmeid of Arsal detained two men, Omar Mohamed Othman and Radwan Mahmud Ayyush, of Syrian nationality," the army said.
The statement said the two men were detained for "entering Lebanese territory illegally," adding they were being held for questioning.
Ayyush, a former captain in Syria's army, joined his country's rebellion at an unknown date, and became a commander in the opposition's military council in Qusayr, a former rebel stronghold near Lebanon's border.
After a year-long siege, Qusayr fell from rebel hands in June last year after Syrian troops backed by Lebanese Shiite Hezbollah fighters launched a blistering offensive.
Speaking to AFP via the Internet, an opponent from Qusayr said he did not know what role, if any, Ayyush plays today in the rebellion.
Once dominated by Damascus militarily and politically, multi-sectarian Lebanon is deeply divided over the Syrian war, with Sunnis backing the Sunni-led revolt and Shiites largely supporting the Assad regime.
The divisions have widened since Hezbollah acknowledged last May that it was sending fighters into Syria to support Assad's troops.