Russian servicemen salute as air force pilots arrive to board a Russian Sukhoi Su-30SM fighter jet before departure on a mission at the Russian Hmeimin military base in Latakia province, in the northwest of Syria, on December 16, 2015.

MOSCOW, Nov. 14 (Xinhua) -- The Russian Defense Ministry on Tuesday accused the U.S.-led coalition of interfering with the Russian air force to protect retreating Islamic State (IS) militants.

The militants had been forced to retreat from the city of Abu Kamal in the Syrian province of Deir al-Zour, one of the last remaining IS strongholds in Syria, by the advancing government troops.

In violation of a previously reached agreement, attack aircraft of the coalition entered the airspace over Abu Kamal to hamper the work of the Russian air force, the ministry said in a statement.

"Such actions by the coalition show that the rapid advance of the Syrian troops in Abu Kamal have disrupted U.S. plans to create pro-American authorities beyond the control of the Syrian government, and to manage the territories on the eastern bank of the Euphrates," it said.

The ministry also said that the U.S. coalition categorically refused to strike the retreating terrorists in spite of repeated proposals by the Russian military to conduct joint actions.

The U.S. military said the militants were voluntarily surrendering and so fell under the provisions of the Geneva Convention on the treatment of prisoners of war.

But they did not provide any answer to the query why heavily armed IS militants were regrouping in the zone under the control of the international coalition for new attacks on Syrian troops, the ministry said.

"These facts give indisputable evidence that the U.S., which (pretends) before the world community an irreconcilable fight against international terrorism, in fact provides cover for combat-capable IS units to restore their forces, regroup and be used for promoting U.S. interests in the Middle East," the statement said.

Russia and the U.S.-led coalition are backing separate offensives against the IS in Syria, with both advancing in oil-rich Deir al-Zour in the east of the war-torn country.