US President Donald Trump on Monday dismissed Iran's claim it had captured 17 spies working for America's Central Intelligence Agency.
Iran state television reported the Intelligence Ministry had uncovered a CIA spy ring. The semi-official Fars news agency, quoting ministry officials, said some of those arrested had been sentenced to death.
Mr Trump tweeted: "The report of Iran capturing CIA spies is totally false. Zero truth."
Secretary of State Mike Pompeo also dismissed Iran’s claims, telling Fox News “the Iranian regime has a long history of lying".
"I would take with a significant grain of salt any Iranian assertion about actions that they've taken," he said.
Mr Pompeo declined to comment about any specific cases. "There's a long list of Americans that we are working to get home from the Islamic Republic of Iran," he added.
The arrests took place in recent months and those taken into custody worked on “sensitive sites” in the country’s military and nuclear facilities, an Iranian intelligence official told a press conference in Tehran.
He did not elaborate, say how many of them were sentenced to death, or when the sentences were handed down.
The announcement comes at a time of heightened tension between the US and Iran.
In May, US President Donald Trump pulled out of the 2005 nuclear deal and reimposed sanctions on Iran. In recent months, the US has blamed Iran for several attacks on oil tankers near the Strait of Hormuz and Revolutionary Guards also shot down an American drone.
The Iranian official did not give his name but was identified as the director of the counterespionage department of Iran’s Intelligence Ministry. Such a procedure is highly unusual in Iran; officials usually identify themselves at press conferences. It is also rare for intelligence officials to appear before the media.
The official claimed that none of the 17, who allegedly had “sophisticated training,” had succeeded in their sabotage missions. Their spying missions included collecting information at the facilities they worked at, carrying out technical and intelligence activities and transferring and installing monitoring devices, he said.
Although there was no confirmation that it is the same group accused of being a CIA ring, last month, Iran said it had penetrated an American espionage operation in Iran and other “allied countries”.
The state-run IRNA news agency reported that the country’s intelligence agencies had “penetrated the US safe system in cyber-space” that was used “for maintaining communication with spies".
State broadcaster IRIB reported Ali Shamkhani, the secretary of the country’s Supreme National Security Council, said the information was passed to allies.
“We provided the information on the exposed network to some other allied countries in which it had been operating, which resulted in the exposing and dismantling of the US intelligence officers network and arrest and conviction of some CIA agents in different countries,” Mr Shamkhani said.
IRNA reported intelligence officials said those arrested were working as contractors and consultants in vital private-sector companies, including nuclear, military and cybersecurity firms.
The official said the detainees had been recruited in exchange for a US visa and the promise of relocation in the West.
The official also appeared to suggest some of those arrested had been attempting to flee the country and went to meet CIA handlers in border areas when they were apprehended by Iranian intelligence waiting for them.
IRNA said the official claimed that as some of those recruited had been approached at international conferences in Europe and Africa and Iranian intelligence would hold those countries responsible for any CIA recruitment that took place in their country.