The United States and its European allies said that Iran was “in defiance of” a United Nations Security Council resolution when the Islamic Republic launched nuclear-capable missiles in March.

A joint American-European letter sent to Spanish Ambassador to the U.N. Roman Marchesi and U.N. Secretary-General Ban Ki-moon, who represent the Security Council, requested a discussion about “appropriate responses” to Tehran’s violation. The U.S., United Kingdom, France, and Germany said the missile tests are “destabilizing and provocative.” The missiles, added the letter, are “inherently capable of delivering nuclear weapons,” the Associated Press reported Tuesday.

U.N. Security Council Resolution 2231, adopted last July, endorsed the nuclear deal between Iran and world powers but banned missiles tests such as those that Iran recently conducted. Iran’s Islamic Revolutionary Guard Corps said the missile tests were meant to “show Iran’s deterrent power and also the Islamic Republic’s ability to confront any threat against the [Islamic] Revolution, the state, and the sovereignty of the country.”