BEIRUT, Lebanon — Lebanese security forces on Sunday arrested a radical Islamic cleric who was long prominent in Britain and was wanted here under a new security plan to curb violence in the northern city of Tripoli that has been exacerbated by the war in neighboring Syria.

The cleric, Omar Bakri Muhammad, was arrested in the town of Aley, according to the National News Agency. He had been on the run since April, when security forces raided his house in Tripoli.

Mr. Bakri, who was born in Syria, preached for years in London, where he helped found Al Muhajiroun, a radical Islamist group that was banned and reconstituted itself as Hizb-ut-Tahrir. He moved to Lebanon in 2005 and has been barred from returning to Britain.

Lebanese authorities viewed him with increasing concern after he expressed support for an extremist group that has taken over parts of northern Syria, the Islamic State of Iraq and Syria, and called for it to activate cells in Lebanon. He has denied ties to Al Qaeda, but has called for the group’s flag to be flown over Lebanon’s presidential palace.