"We are making progress, yeah. We're making progress," he told reporters when asked whether there is any indication that EU is closer to imposing sanctions to block Iran's missile progress.
Europeans have become increasingly aware of the threat that Iran poses, and about associated steps to address the issues outside of the nuclear deal, Hook said.
"The nuclear deal, from its inception in the last administration, was never meant to be an obstacle to address any other threat that Iran presents to peace and security," Hook told reporters.
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Last week, US Secretary of State Mike Pompeo said that Iran had test launched a medium-range ballistic missile that was capable of carrying multiple warheads in violation of UN Security Council resolutions. Tehran responded by saying that the Iranian missile program was defensive in nature and developed in accordance with the needs of the country.
A number of the UN Security Council's resolutions and the Joint Comprehensive Plan of Action ban Iran from any activities, deals and transfers related to the development of ballistic missiles.