Jihadist forums on Saturday distributed a recording by a previously unknown figure announcing the creation of a Lebanese franchise for the Islamic State of Iraq and the Levant (ISIL).
In the recording, Abu Sayyaf al-Ansari swears allegiance to Abu Bakr al-Baghdadi, the Iraqi leader of ISIL, which has its roots in Al-Qaeda in Iraq and emerged in Syria last spring.
He also called on Sunnis to abandon the Lebanese "crusader" army, echoing allegations by Sunni Islamists that the armed forces are "backed by Hezbollah."
The recording emerged amid spiralling sectarian tensions in Lebanon linked to the war in neighbouring Syria.
While Lebanon's Shiite Hezbollah has sent troops to Syria to back President Bashar al-Assad, many Sunnis support the revolt against him.
"We pledge allegiance to the prince of the believers, Abu Bakr al-Baghdadi... and we ask him to guide us past the obstacles, and make us your spearhead in crushing your enemy, and not a single man among us will hold back in helping you," said Ansari.
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In the five-minute recording, he said "a spokesman for ISIL in Lebanon" identified as Abu Omar al-Muhajir would soon make a statement of his own.
ISIL emerged in Syria last year, seizing large swaths of rebel-held territory and imposing a harsh version of Islamic law.
Though the jihadists were initially welcomed by Syria's rebels, their quest for hegemony and brutal attacks on rivals and activists led several powerful rebel groups to turn on them earlier this month.
Ansari also congratulated the Abdallah Azzam Brigades, an Al-Qaeda-linked group that claimed responsibility for a twin suicide attack in November against the Iranian embassy in southern Beirut, a Hezbollah stronghold, which killed 25 people.
But he said such groups "alone were insufficient."
He said his pledge comes from mostly Sunni Tripoli, Lebanon's second city, which has seen frequent battles pitting Sunni militants against Alawites, who come from the same offshoot of Shiite Islam as Syria's Assad.