The US-led coalition fighting the Islamic State group is prepared to support Turkish forces battling the fighters in northern Syria, a US military official said Wednesday.

Turkey has asked for such assistance from the coalition but none has been forthcoming so far.

Colonel John Dorrian, speaking via video conference from Baghdad, said support will be offered.

"I can confirm for you that those discussions have been happening and the Turks are aware of some of the things that might be in store," Dorrian said, declining to provide further details.

Turkish forces have been engaged for several weeks in deadly fighting against the Islamic State group to retake the Syrian city of Al-Bab.

But despite Turkish President Recep Tayyip Erdogan's requests, coalition planes have not been deployed to directly help the Turks.

Coalition aircraft did make a show of force last week near Al-Bab at the request of Turkish forces but did not fire any weapons.

The coalition criticizes Turkey for launching the offensive unilaterally without first reaching an agreement with its partners.

The Americans supported the first part of the Turkish offensive in Syria in mid-2016.

Neither the coalition nor Turkey have said why the coalition stopped supporting Turkish forces in Syria as they did at the start of the Turkish offensive in August.

But US officials have suggested they are concerned that the Turks, after the conquest of Al-Bab, might attack the Kurdish-led Arab-Kurdish coalition of the Syrian Democratic Forces.

The United States sees the SDF as their most effective ally in the fight against Islamic State in Syria. The SDF is currently leading the first part of the offensive against Raqa, the self-proclaimed IS capital in Syria.

The United States is walking a thin line in these discussions with Turkey, as Ankara it is a key ally of the coalition, allowing it to use the Turkish air base at Incirlik for attacks against jihadists.