WASHINGTON (Reuters) - U.S. and Russian military officials signed a memorandum of understanding on Tuesday that includes steps their pilots should take to avoid an inadvertent clash over Syria as they carry out separate air strikes against militant groups, the Pentagon said.

The issue of aircraft safety started after Russia began bombing targets in Syria last month. Moscow says it is attacking Islamic State, but many of its air strikes have hit territory held by other rebel groups fighting against Russia’s Syrian ally, President Bashar al-Assad.

Pentagon spokesman Peter Cook said the full text of the memo would not be released at Russia’s request, but it included specific protocols for air crews to follow, plus the creation of a ground communications link between the two sides in the event air communications fail.

Earlier this month the Pentagon said U.S.-led coalition aircrafts bombing Islamic State in Syria were re-routed at least once to avoid a close encounter with Russian planes.

“The U.S. and Russia will form a working group to discuss any implementation issues that follow,” Cook said during a press briefing.

Cook told reporters later the memo was signed for the U.S. side by Army General Lloyd Austin, the head of U.S. Central Command, which is responsible for U.S. forces in the Middle East region.

He said the document called for U.S. and Russian aircraft to maintain a safe distance, but he declined to be more specific about whether the protocols included specific distances.

He added that the agreement covered coalition aircraft. Coalition members include Saudi Arabia, Turkey and the United Arab Emirates.

“The fact that we have had to resort to a memorandum of understanding…gives you an indication of our concern about Russia’s activities but (also) our willingness to work with the Russians when it’s in our own interest,” Cook said.

The U.S. State Department said the agreement is only about keeping pilots safe.

“It’s not a treaty of cooperation or anything like that ... It doesn’t connote cooperation or coordination or joint targeting,” State Department spokesman John Kirby said.

On Tuesday Moscow said it had received a memorandum from the U.S. military on preventing mid-air incidents over Syria.(nL8N12K3Z7)