TEHRAN, Iran — Senior Iranian lawmakers stepped up threats Monday that Islamic Republic warships could block the Persian Gulf’s oil tanker traffic after the latest blow by Western leaders seeking to rein in Tehran’s nuclear program: A punishing oil embargo by the European Union that sharply raises the economic stakes for Iran’s defiance.

The EU decision in Brussels — following the U.S. lead to target Iran’s critical oil exports — opened a new front against Iran’s leadership. Pressure is bearing down on the clerical regime from many directions, including intense U.S. lobbying to urge Asian powers to shun Iranian crude, a nose-diving national currency and a recent slaying in what Iran calls a clandestine campaign against its nuclear establishment.

In response, Iranian officials have turned to one of their most powerful cards: the narrow Strait of Hormuz at the mouth of the Gulf and the route for a fifth of the world’s oil. Iran has rattled world markets with repeated warnings it could block the hook-shaped waterway, which could spark a conflict in the Gulf.

Military experts have questioned whether Iran has the naval capabilities to attempt a blockade. But, the U.S. and allies have already said they would take swift action against any Iranian moves to choke off the 30-mile wide strait — where the American aircraft carrier USS Abraham Lincoln, along with British and French warships, entered the Gulf on Sunday without incident.

The British Ministry of Defense said the three nations sought to “underline the unwavering international commitment to maintaining rights of passage under international law.”

Earlier this month, Gen. Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, told CBS’ “Face the Nation” that Iranian forces could block shipping through the strait “for a period of time,” but added “we can defeat that” and restore the flow of oil and other commerce. He did not offer details on a U.S. military response, but the Pentagon is believed to have contingency plans for such a scenario.

A member of Iran’s influential national security committee in parliament, Mohammad Ismail Kowsari, said Monday that the strait “would definitely be closed if the sale of Iranian oil is violated in any way.” He went on  to warn the U.S. against any “military adventurism.”

Another senior lawmaker, Heshmatollah Falahatpisheh, said Iran has the right to shutter Hormuz in retaliation for oil sanctions and that the closure was increasingly probable, according to the semiofficial Mehr news agency.