Moscow says it is halting an agreement with Washington aimed at avoiding mid-air collisions during their military missions in the Syrian airspace after US launched a missile attack against a Syrian army airbase.

“The Russian side is halting the effect of the memorandum for prevention of incidents and ensuring safety of air flights during operations in Syria which was agreed with the US,” said a statement by the Russian Foreign Ministry on Friday. It was referring to the 2015 agreement, under which Russia and the US agreed to exchange information on their flights in Syrian skies, where the two sides have been involved in separate military operations.

The announcements came after some 60 US Tomahawk missiles were fired from US warships deployed to the Mediterranean at the Shayrat airfield southeast of the western Syria city of Homs earlier in the day. Russian Defense Ministry pledged to beef up Syrian air defenses following the attack. It also played down the effectiveness of the US raid, saying 23 missiles had hit their targets while it was unclear where 36 others had landed.

Washington ordered the assault after accusing Syria of carrying out a chemical attack against the town of Khan Sheikhun in the northwestern province of Idlib on Tuesday. The Russian Foreign Ministry statement said, “Obviously, the cruise missile attack was prepared beforehand. Any expert can tell that the decision to strike was made in Washington before the events in Idlib, which were used as a pretext for a demonstration.”