The Syrian Observatory for Human Rights told Reuters on Tuesday that it had "confirmed information" that Islamic State leader Abu Bakr al-Baghdadi has been killed.

Russia's defence ministry said it may have killed Baghdadi when one of its air strikes hit a gathering of Islamic State commanders on the outskirts of the Syrian city of Raqqa, but Washington said it could not corroborate the death and Western and Iraqi officials have been sceptical.

Reuters could not independently verify Baghdadi's death.

Baghdadi's death, which has been frequently reported since he declared a caliphate from a mosque in the Iraqi city of Mosul in 2014, is one of the biggest blows yet to the jihadist group, which is trying to defend shrinking territory in Syria and Iraq.