Lebanon's army on Wednesday arrested a commander of Syria's Al-Nusra Front, a branch of Al-Qaeda and ally of rebels fighting to bring down President Bashar al-Assad, a security official told AFP.
"Army intelligence arrested an Al-Nusra commander in the region of Masharia al-Qaa," which borders Syria, the source said on condition of anonymity.
An army spokesman confirmed the report.
"A man suspected of being an Al-Nusra Front commander was arrested in the east of the country," the spokesman said, adding: "He is being interrogated."
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Al-Nusra Front brings together Syrian and foreign jihadists. It has become an increasingly prominent player in Syria's war over the past year.
It is staunchly opposed to the regime in Damascus but also to its ally in Lebanon, Hezbollah, which has dispatched thousands of fighters into Syria to join Assad's troops.
The Lebanese army frequently arrests Lebanese, Palestinians and Syrians suspected of links with extremist groups that have claimed responsibility for a wave of deadly bomb attacks targeting Hezbollah bastions.
The army has also jailed gunmen found near the Lebanese-Syrian border, and defused car bombs.
Extremist groups such as the Abdullah Azzam brigades and Al-Nusra Front in Lebanon -- believed to be linked to the Syrian Qaeda branch -- have claimed recent attacks, blaming Hezbollah for entering the Syrian war.
Syria's conflict has exacerbated Lebanon's sectarian and political divisions, with most Shiites backing Hezbollah and most Sunnis supporting the rebels.