LONDON — Iran said on Monday that it had arrested 17 Iranian citizens on charges of spying for the United States and had already executed some of them, Iranian and Western news media reported.
At a news conference in Tehran, an official who identified himself as a director of counterespionage in the Intelligence Ministry described the arrests of people he said had been trained by the C.I.A., but he did not name them and gave few details of their alleged spying. The official declined to give his name, The Associated Press reported, and did not say how many of those arrested had been killed.
Iran has previously claimed, without elaboration or supporting evidence, to have broken up American spy rings. It made similar announcements in April and again in June this year.
The latest claim comes at a moment of rising tensions between Iran and the West.
Tehran and Washington are in a showdown over President Trump’s withdrawal from the 2015 nuclear accord that Iran signed with several international powers and over his imposition of sweeping new sanctions in an attempt to force Tehran to negotiate a new agreement. In response, Iran has ramped up its nuclear program in recent months, exceeding limits imposed by the deal.
Against that backdrop, Iran on Friday seized a British-flagged oil tanker entering the Persian Gulf through the Strait of Hormuz. Iran has accused the tanker of various infractions but also described the seizure as retaliation for the British impounding of an Iranian tanker on July 4 off the coast of Gibraltar.
Britain has said that it detained the Iranian tanker on suspicion that it was violating a European Union embargo on the delivery of oil to Syria. Foreign Minister Jeremy Hunt has called it a tanker “tit-for-tat,” and the British government has threatened “serious consequences” and “robust” action if Iran does not release the British ship.
Prime Minister Theresa May, who is expected to leave office on Wednesday, held the latest in a series of emergency cabinet meetings on Monday to address the tanker seizure.
A race within the Conservative Party to succeed her is nearing its completion. The favorite is Boris Johnson, a former foreign minister who has not publicly expressed an opinion about the crisis. He has styled himself as a populist and a nationalist, and analysts say his response is hard to predict.
In May and June, six tankers from various nations were damaged in the Gulf of Oman, in what United States officials described as attacks by Iran. Iran denied responsibility. The gulf connects to the Strait of Hormuz, through which about 20 percent of the world’s oil supply flows.
Last month, Iran shot down an American surveillance drone that it said had violated its airspace, but which the United States said was over international waters, prompting President Trump to order airstrikes that he then called off at the last minute.
A running battle to root out American spies is a staple of the news media in Iran. The English-language Press TV in the country recently broadcast a documentary about what it called a successful “mole hunt” for C.I.A. agents.
According to a BBC report, the Iranian intelligence minister, Mahmoud Alavi, said in the documentary that the spy hunt had resulted in the C.I.A. “crumbling like a house of cards.” The documentary argued that President Trump was making “wrong and bizarre” decisions about Iran and suggested that the reason may be “a lack of access to reliable intelligence.”
A fictional Iranian television series, called “Gando,” that reached its conclusion this month, chronicled the exploits of heroic counterintelligence agents battling a villainous American spy working under cover as a journalist.
The director and producer have reportedly said that the series is based on the case of Jason Rezaian, a reporter for the Washington Post who spent 18 months in an Iranian prison on charges of espionage, which he and American officials denied.
In a post on Twitter, Mr. Rezaian said the resemblance was only superficial. “Besides being fat, bald and wearing glasses, there is no similarity to me or anything that has happened in my life,” he wrote on June 25.
Iranian news agencies also reported last month that Iran had executed a man arrested two years earlier, Jalal Hajizavar, who was accused of being a spy for the United States. He was said to have been a former employee of the Iranian Defense Ministry’s Aerospace Industries Organization who had been fired years earlier.
The semiofficial news agency Fars said that Mr. Hajizavar had “explicitly confessed that he had collaborated with the C.I.A. and spied for the United States in return for money.” It also reported that his spouse had been sentenced to 15 years in prison for cooperating with him.
The Iranian fear of American spies is founded in history. American intelligence agencies have used cyberweapons to disrupt Iran’s nuclear program. And all Iranians know that in 1953, the C.I.A. orchestrated a military coup that removed an elected prime minister.