Washington on Thursday accused Iran of carrying out three missile-related launches in defiance of United Nations resolutions and said the Security Council should “bring back tougher international restrictions” against Tehran.

US acting Ambassador Jonathan Cohen warned in a letter to the council that Iran’s activities were destabilizing the entire region and could trigger an arms race.

Cohen highlighted a December 1 launch of a medium-range ballistic missile and the January 15 and February 5 attempts by Iran to send satellites into orbit using space launch vehicles.

“Iran has carried out these three launches in defiance of the expressed will of the UN Security Council, and such provocations continue to destabilize the entire Middle East region,” said the letter.

Washington called on the council to “join us in imposing real consequences on Iran for its flagrant defiance of the council’s demands and bring back tougher international restrictions to deter Iran’s missile program.”

There was no immediate request from Washington for a council meeting to discuss Iran and no further steps were announced in the letter.

UN Security Council Resolution 2231, which was adopted just after the 2015 nuclear deal, calls on Iran “not to undertake any activity related to ballistic missiles designed to be capable of delivering nuclear weapons.”

Tehran insists that its missile development program is defensive and in compliance with the resolution, but Washington has repeatedly challenged that position.

In the letter, the acting ambassador said the December 1 launch was “designed to be capable of delivering nuclear weapons” and that the space launch vehicles use technologies that are “virtually identical and interchangeable” with those used by ballistic missiles.

“Iran’s January 15 and February 5 satellite launches constitute activities using technologies related to ballistic missiles designed to be capable of delivering nuclear weapons,” wrote Cohen.

“The prospect of rapid escalation in the region is real, and increasingly likely, if we fail to restore deterrence.”

– with reporting by Agence France-Presse