Hook addressed the press on his way to a summit of top NATO officials in Brussels.

US Secretary of State Mike Pompeo is scheduled to meet with leaders from Germany, France and the United Kingdom, all of whom were part of the negotiations behind the 2015 Iran nuclear accord, which the US withdrew from in May.

“This is a continuing discussion that the secretary has had with his E3 counterparts about Iran’s missile testing and missile proliferation and regional aggression,” said Hook. “I believe that we are making progress toward getting a proposal tabled in Brussels that would designate the individuals and the entities that are facilitating Iran’s missile program.”

“It is a grave and escalating threat, and nations around the world—not just Europe—need to do everything they can to be targeting Iran’s missile program,” he added.

This development comes as Iran test-fired a ballistic missile on Saturday “that is capable of carrying multiple warheads” and “violates UN Security Council resolution 2231 that bans Iran from undertaking ‘any activity related to ballistic missiles designed to be capable of delivering nuclear weapons, including launches using such ballistic-missile technology,’ ” Pompeo said that day.

“As we have been warning for some time, Iran’s missile testing and missile proliferation is growing. We are accumulating risk of escalation in the region if we fail to restore deterrence,” he added. “We condemn these activities and call upon Iran to cease immediately all activities related to ballistic missiles designed to be capable of delivering nuclear weapons.”