Tehran’s skyline in 2016. (Gabriela Baczynska/Reuters)

President Trump on Monday denied Iran’s claim that it dismantled an elaborate U.S. spy ring tasked with monitoring key military sites, dismissing the reports as a “totally false story” amid rising tensions between Tehran and the West. 

Iran said that its intelligence forces identified and arrested 17 Iranians suspected of spying for the CIA and that some of them have been sentenced to death. The announcement adds to concerns about Tehran’s nuclear program and its efforts to impede shipping traffic through the Strait of Hormuz. 

British Foreign Secretary Jeremy Hunt announced on Monday the formation of a joint European “maritime protection mission” to ensure safe transit in the strait, a key waterway for global oil shipments. 

Iran last week seized a British-flagged oil tanker that it said had “violated maritime rules,” following the detention of an Iranian vessel off the coast of Gibraltar earlier this month. 

Speaking to lawmakers in the House of Commons, Hunt said his government will ask that all British-flagged vessels intending to navigate the Persian Gulf, near the Strait of Hormuz, give notice so they can be protected in the passage.

Hunt said that it was not possible for every such vessel to be escorted but that ships might proceed through the strait in convoys. He also announced that Britain has raised the maritime warning to Level 3, “advising against all passage in Iranian waters and, for the moment, in the entire Strait of Hormuz.”

At a news conference in Tehran, an Iranian counterintelligence official said his forces uncovered a network of spies recruited by CIA agents to monitor vital infrastructure in Iran, including its military and nuclear sites. The official, who was not identified, gave few specifics on the nature of the alleged spying but said the suspects were trained to set up encrypted communication channels and to destroy documents if their cover was blown. 

He claimed that the suspects were arrested in cities on the border, where, he said, they had traveled to meet their foreign intelligence handlers. They encountered Iranian counterintelligence officers instead, he said. 

He did not give the names of the suspects, and it was unclear which members were sentenced to death and for what alleged activities. He said that the arrests were made during the Persian calendar year ending in March and that those detained were recruited on social media networks, on the sidelines of scientific conferences abroad and while applying for visas at U.S. diplomatic missions. 

As evidence, state media published what it said were photos, business cards and cellphone numbers of the alleged handlers. 

The photographs appeared to be taken from social media sites. Some of the individuals do hold diplomatic positions, according to public records. The cards of two of the officials said they were posted to Vienna, a diplomatic crossroads that has long been a focus of U.S. intelligence activity targeting Iran, with mixed results.

Iran’s semiofficial news agency, Fars, citing what it claimed was a senior Iranian intelligence official, appeared to try to bolster the credibility of the government’s claims by reporting accurate details of previous CIA activities in Iran.

For instance, Fars referred to an earlier compromise of the CIA’s spy networks in 2013 that current and former officials have said did occur. The Fars report also gave accurate descriptions about how Iran disrupted the covert communications systems the CIA has used to communicate with agents in the country and the plans that the agency put in place to evacuate its Iranian spies in case they were discovered.

The CIA’s “spies had been trained and in case of danger, they should have contacted CIA and reach out to specific points in border cities, then wait for the presence of CIA bridge agent to follow his/her leads for evacuation,” Fars reported.

Secretary of State Mike Pompeo, who formerly served as CIA director, called the reports false. 

“The Iranian regime has a long history of lying,” Pompeo said in an appearance Monday on Fox News’s “Fox & Friends” program. “I would take with a significant grain of salt any Iranian assertions about actions that they’ve taken.” 

A CIA spokesman declined to comment on Iran’s claims or any of the agency’s operations.

This was not the first time that Iran has claimed to have captured spies working for the United States, and the announcement was being read by current and former officials in Washington as, at least partially, a domestic propaganda effort to bolster the image of Iranian spy hunters as smarter than their American adversaries.

In 2005, journalist James Risen reported that the CIA enlisted a former Soviet nuclear engineer and defector to deliver blueprints for a nuclear-triggering device to Iran’s mission of the International Atomic Energy Agency, headquartered in Vienna. The blueprints were deliberately flawed, and the CIA hoped that Iran would waste years trying to build the component. Risen reported that the flaw was not well hidden and that Iran could still use portions of the design to accelerate its nuclear weapons program.

The George W. Bush administration was so unnerved by the revelation that White House aides considered trying to persuade Risen’s publisher from halting release of his book detailing the covert operation, code-named Merlin, according to former U.S. officials. In 2015, a federal jury found former CIA officer Jeffrey Sterling guilty of leaking classified information about the program to the journalist.

Also Monday, the State Department said it will sanction China’s chief trader in Iranian oil, state-owned Zhuhai Zhenrong, and its top executive, Youmin Li, citing violations of U.S. restrictions on Iranian oil sales.

China has continued to import Iranian oil, despite the U.S. pressure campaign to deprive Iran of its main source of foreign income. Most other countries have stopped, acquiescing to U.S. demands to cut their Iranian oil imports to zero.

“We’ve said that we will sanction any sanctionable behavior, and we mean it,” Pompeo said in a speech at a Veterans of Foreign Wars convention in Orlando during which he announced the measures.

Booth reported from London. Shane Harris, John Wagner and Carol Morello in Washington contributed to this report.