The British broadcaster said the military -- with assistance of area tribesmen loyal to the Iraqi government -- had begun searching for al-Qaida leaders in Mosul as part of Operation Lion's Roar.

The city in northern Iraq has long been seen as the last stronghold for al-Qaida operatives in Iraq and a military operation in the city had been expected, the BBC said.

Iraqi Prime Minister Nouri al-Maliki has said al-Qaida has been gradually weakening in Iraq to the point it could soon be removed from Iraq altogether.

The BBC said the new military operation was initiated following reports that al-Qaida leader Abu Ayyub al-Masri was arrested in Mosul. U.S. officials denied the al-Qaida official had been arrested.