The U.S. Department of Defense said on Tuesday that Turkey will not be able to acquire U.S. missile batteries until it returns a Russian air-defense system.

“Turkey is not going to receive a Patriot battery unless it returns the S-400,” said a Pentagon spokesperson in a reiteration of U.S. policy.

In February, Turkey requested that the United States send two Patriot batteries to its southern border to deter any future attacks by Syrian troops.

The request was made in the aftermath of violence on Feb. 20, which left two Turkish troops dead and five wounded killed in an airstrike in the rebel-held Idlib province, as pro-Syrian forces have tried to retake the area that is the last one held by those opposed to the regime of Syrian President Bashar Assad.

Turkey acquired the S-400 missile-defense system last year in a move that caused the United States to eject it from the F-35 program.

In a tweet, American Friends of Kurdistan co-founder Diliman Abdulkader affirmed that the Pentagon announcement is: “How it should be. And don’t expect Turkey to return the S-400, Putin has a no return/exchange policy.”