A Syrian cleric who recruited foreign fighters travelling to Iraq to fight U.S.-led forces was assassinated in the northern Syrian city of Aleppo on Friday, an aide said.

Sheikh Mahmoud Abou al-Qaqa was shot dead after he emerged from Friday prayers, Ahmad Haidar told Reuters.

"A man fired several bullets into the Sheikh's chest. A crowd chased him and he was eventually caught. He is now with the authorities under custody," Haidar said.

Qaqa had thousands of followers and operated in the mysterious world of Islamist movements in Aleppo, a once liberal trading hub that has become more religious in recent years.

The 42-year cleric had called for jihad, or holy war, to counter U.S. policies against Syria. Experts say he toned down his rhetoric lately and became less active.

The Syrian government is accused by Washington and the pro-U.S. government in Baghdad of helping foreign fighters behind sectarian killings and attacks on U.S. soldiers.

Damascus denies helping rebels.