The US-led coalition bombing the Islamic State group in Syria needs better communication with the Russian military and other regional players, a top US Air Force general said Friday.

General Herbert "Hawk" Carlisle, who heads the Air Combat Command, said air space is getting increasingly congested as IS loses territory and efforts against the group focus on smaller areas.

"By definition, as we take battle space away from ISIS, that creates more conflict potential between us and the other players in the theater," Carlisle told reporters in Washington.

After Russia began bombing in Syria in late 2015 to prop up the regime of President Bashar al-Assad, the US-led coalition and Moscow established a "deconfliction" hot line designed to prevent midair mishaps.

The line has proven imperfect, however, with delays and miscommunications causing problems on the ground on at least one occasion.

"Increased deconfliction discussions, increased dialogue, has got to happen because it's going to become more and more complex as time goes on," he said.

Carlisle's comments come after Lieutenant General Jeffrey Harrigian told reporters in Baghdad this week that the coalition and Russia need to loop senior officers into communications.

Currently, the hot line is manned by a US colonel and his Russian equivalent.

Last week, Chairman of the US Joint Chiefs of Staff Joe Dunford and his Russian counterpart Valery Gerasimov discussed military relations between the two countries.

The two sides undertook "efforts to improve operational safety of military activities in order to decrease the prospects for crisis and avoid the risk of unintended incidents," the Pentagon said in a statement.

President Donald Trump had indicated he was open to greater military cooperation with Russia in the IS fight, but senior US military leaders have been quick to steer him from that goal.

In addition to Russia, the coalition and the Syrian regime, Turkey is also flying warplanes over Syria and on Friday, Iraq conducted an anti-IS strike inside Syria.

Separately, Carlisle updated reporters on the progress of the Air Force's version of the F-35 stealth fighter.

He said it would likely be deployed to Europe "in the spring to summer time" this year.

The Air Force also has plans to send it to the Pacific and the Middle East in the "not too distant future."