US military spokesman denies claims the Pentagon is communicating with Assad regime via Kurdish intermediaries.

US Air Force has been hitting ISIS targets in and around Hasakeh

The US military flatly denied Tuesday a claim from a Kurdish militia source that it coordinates air strikes against ISIS in Syria with Bashar al-Assad's regime forces.

Both Syrian and US-led coalition planes have been seen in recent days over Hasakeh in northern Syria, where the so-called Islamic State is battling local Kurdish fighters.

An officer in the town with the YPG Kurdish militia, speaking on condition of anonymity, told AFP that the two air forces "communicate through a Kurdish mediator."

But a US military spokesman insisted that this is not the case.

"US aircraft are not coordinating in any way with Syrian government assets, neither directly or through an intermediary, nor have we in the past," Major Curtis Kellogg of US Central Command told AFP.

The United States and some of its allies are engaged in an aerial bombing campaign targeting ISIS on the territory it has carved out in Iraq and Syria.

In Iraq, the strikes are conducted with the approval and cooperation of the Iraqi government, which is itself locked in a fierce ground conflict with the jihadists.

But the situation is more complicated in Syria, where US air strikes are conducted to "degrade and ultimately destroy" ISIS and to assist some Kurdish and rebel factions, but not to support the Assad regime.