Muhsin al-Fadhli is seen in an undated photo provided by the U.S. State Department in Washington, D.C. A long-time al Qaeda operative and key figure in the Khorasan Group, Muhsin al-Fadhli, was killed in a U.S. air strike while traveling in a vehicle near Sarmada, Syria, on July 8, the Pentagon said in a statement on July 21, 2015. Photo: REUTERS/State Department/Handout via Reuters

A US air strike has reportedly killed Muhsin al-Fadhli, the Kuwaiti leader of the Khorasan Group, a shadowy al-Qaeda offshoot operating in Syria.

Al-Fadhli was targeted on 8 July while travelling in a vehicle near Sarmada in Syria, a Pentagon spokesman said.

A statement by US Navy Capt Jeff Davis said al-Fadhli was one of the few al-Qaeda leaders to have known in advance of the 9/11 attacks.

Al-Fadhli was also said to have been targeted in a US strike last September.

Some initial reports had suggested al-Fadhli was killed in the earlier attack, which took place west of the Syrian city of Aleppo.

Very little was known about the Khorasan Group until the US military claimed to have bombed its facilities last September.

The group's leaders are said to have comprised veterans of al-Qaeda campaigns in Afghanistan and Pakistan.

US officials said they had been sent to Syria by al-Qaeda's leader, Ayman al-Zawahiri, in order to recruit jihadists with Western passports for bombing missions.

The militants are thought to have embedded themselves within al-Qaeda's Syrian affiliate, the al-Nusra Front, operating out of premises in its strongholds.

The US State Department had offered a $7m (£4.5m; €6.4m) for information leading to al-Fadhli's capture or death.