A Hezbollah-run media unit said on Friday Abu Bakr al-Baghdadi, leader of the Islamic State in Iraq and Syria (ISIS), was reported to have been in the Syrian town of Boukamal during the Syrian army and its allies' operation to clear it.

The military unit did not say what had happened to al-Baghdadi, give further details, or identify its sources.

The U.S.-led coalition against ISIS said on Friday it had no "releasable information" on Baghdadi's whereabouts.

Syria's army declared victory over ISIS on Thursday, saying its capture of the jihadists' last town in the country marked the collapse of their three-year rule in the region. But the army and its allies are still fighting the militant group in desert areas close to Boukamal near the border with Iraq, the Syrian army said on Thursday.

On Friday, the Syrian Observatory for Human Rights said Islamic State has taken back control of half of Boukamal. The capture of the border town had sealed "the fall of the terrorist Daesh organisation's project in the region", an army statement said on Thursday, using the Arabic acronym for ISIS.

An audio message purported to be from al-Baghdadi was released in September. He declared himself caliph and heir to Islam's historic leaders from the great medieval mosque in Iraq's Mosul in 2014.