US and Russian military officials have signed a memorandum of understanding that includes steps their pilots should take to avoid an inadvertent clash over Syria as they carry out separate air strikes against armed groups, the Pentagon said.

The issue of aircraft safety started after Russia started bombing targets in Syria last month.

Moscow says it is attacking the Islamic State of Iraq and the Levant (ISIL), but many of its air strikes have hit territory held by other armed groups fighting against Russia's Syrian ally, President Bashar al-Assad.

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Al Jazeera's Rosiland Jordan, reporting from Washington, said on Tuesday that Pentagon spokesman Peter Cook released few details about the memorandum, purportedly at the request of Moscow.

"Cook said that the Russians did not want the details put out publicly," Jordan said.

"As you might expect, that is making it hard for people to judge whether the memorandum will be effective.

"Having said that, there is now a signed agreement, signed by US and Russian officials, which spells out the rules of the airspace over Syria."

Cook did say that the memorandum 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 US-led coalition aircraft bombing ISIL in Syria were re-routed at least once to avoid a close encounter with Russian planes.

"The US and Russia will form a working group to discuss any implementation issues that follow," Cook said during a press briefing.

Cook said the memo calls for 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 included coalition aircraft. Coalition members include Saudi Arabia, Turkey and the United Arab Emirates.

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"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 US 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 US military on preventing mid-air incidents over Syria.

Source: Al Jazeera And Reuters