TEHRAN, Iran — Senior Iranian lawmakers have stepped up threats 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 taken Monday 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, 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 United States and its 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 said “we can defeat that” and restore the flow of oil and other commerce.

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 warn the United States 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.

“In case of threat, the closure of the Strait of Hormuz is one of Iran’s rights,” Falahatpisheh said. “So far, Iran has not used this privilege.”

The lawmakers’ comments do not directly reflect the views of Iran’s ruling clerics, but they echo similar statements made earlier this month by military commanders with close ties to the theocracy.

At the same time, however, Iran has tried to ease tensions by offering to reopen nuclear talks with the United States and other world powers after a one-year hiatus, and backing off warnings about U.S. naval operations in the Gulf – where the U.S. Navy 5th Fleet has a base in Bahrain.

On Monday in Brussels, the EU’s foreign policy chief, Catherine Ashton, urged Iran to offer “some concrete issues to talk about.”

“It is very important that it is not just about words; a meeting is not an excuse, a meeting is an opportunity and I hope that they will seize it,” she said as the EU adopted its toughest measures on Iran with an immediate embargo on new oil contracts and a freeze of the country’s Central Bank assets. About 90 percent of the EU’s nearly $19 billion in Iranian imports in 2010 were oil and related products, according to the International Energy Agency.

Also Monday, the United States added new sanctions on Bank Tejerat, Iran’s third-largest bank. President Obama has also approved new sanctions on Iran’s powerful central bank that take effect later this year.

It follows U.S. sanctions enacted last month that target the Central Bank and its ability to sell petroleum abroad. The United States has delayed implementing the sanctions for at least six months, worried about sending the price of oil higher at a time when the global economy is struggling.