In a recent piece in Wall Street Journal, Brian Hook, the U.S State Department’s special representative for Iran, said that if the UN refuses to extend the arms embargo on Iran, the US is ready to “snap back all the previous UN sanctions against Iran.

Hook writes: The 13-year-old arms embargo on the Iranian regime will expire in October. The embargo was created by the United Nations Security Council but is scheduled to end because of the 2015 Iran nuclear deal, leaving the world’s foremost state sponsor of terrorism and anti-Semitism free to import and export combat aircraft, warships, submarines and guided missiles. To prevent this, the Security Council must pass a resolution to extend the arms embargo. If this effort is defeated by a veto, the Trump administration is prepared to exercise all legally available options to extend the embargo.

Hook adds that Iranian provocations accelerated under the nuclear deal. Emboldened by repeated diplomatic wins and flush with cash, the Iranian regime increased its ballistic-missile testing and missile proliferation to terrorist proxies. Iran built out a “Shiite crescent” in Syria, Iraq, Lebanon, Bahrain and Yemen, arming its proxies to the teeth.

The U.S. and partners have used the arms embargo to disrupt Iran’s sending advanced weaponry to terrorists and militants. This diplomatic tool has rallied the international community to interdict and inspect weapons shipments, building global condemnation of Iranian violations.

Among many examples, on Feb. 9, a U.S. Navy ship interdicted a ship attempting to smuggle Iranian weapons to Houthi rebels in Yemen. American sailors found 150 antitank guided missiles, three surface-to-air missiles, and component parts for unmanned explosive boats.

According to Brian Hook, the regime plans to upgrade Iran’s aging air force, improve the accuracy of its missiles, and strengthen its ability to strike ships and shoot down aircraft. Iran’s Islamic Revolutionary Guard Corps—a terrorist group with a long history of targeting and killing Americans—could then reverse-engineer technologies in these systems for domestic weapons production and export.

Mr. Rouhani understands the stakes. Last week he appeared on Iranian television to declare that “Iran will give a crushing response if the arms embargo on Tehran is extended.” This threat is designed to intimidate nations into accepting Iran’s usual violent behavior for fear of something worse.

He declared that if American diplomacy is frustrated by a veto, the U.S. retains the right to renew the arms embargo by other means. Security Council Resolution 2231 (2015) lifted most U.N. sanctions but also created a legal mechanism for exclusive use by certain nations to snap sanctions back. The arms embargo is one of these sanctions.