As the US has warned that it would be intensifying its campaign against Islamic State insurgents in the wake of the beheading of American journalist James Foley, the militant group's chief Abu Bakr al-Bagdadi is reported to have fled Iraq for Syria.

A senior Kurdish official has been quoted as saying that al-Bagdadi escaped as part of a convoy on 10 August.

Said Zinni, a spokesperson for the Kurdistan Democratic Party, told the World Tribune: "According to our intelligence sources, Abu Bakr Al-Baghdadi travelled to Syria as part of a convoy of 30 Hummer vehicles after fearing being targeted by US airstrikes."

The claim is yet to be independently verified.

Kurdish officials suspect al-Baghdadi, the self-proclaimed Islamic caliph, has been forced to flee after the killing of many top commanders of the insurgent group in the ongoing US offensive.

Al-Baghdadi was believed to have been operating from Mosul, the first city captured by the Sunni extremists in Iraq.

The US has been pressing ahead with its aerial offensive in the northern parts of Iraq in coordination with Kurdish Peshmerga ground forces which are being equipped with weapons by Nato members.

The attacks are reported to have forced IS to move some of its fighters from northern Iraq to areas in Syria.

"Whoever has authorisation from ISIL is transferred to areas near Mosul. Others are sent to the fighting in Syria after three days of military training at the Kindi training camp," a Kurdish security source was quoted as saying by World Tribune.