US President Donald Trump has dismissed Iran's announcement it had captured 17 spies working for the US Central Intelligence Agency and sentenced some to death.
"The report of Iran capturing CIA spies is totally false. Zero truth," he tweeted.
Iran said the alleged spies had been arrested in the 12 months to March 2019.
Security agencies "successfully dismantled a (CIA) spy network," the head of counter-intelligence at the Iranian intelligence ministry, whose identity was not revealed, told reporters in Tehran.
"Those who deliberately betrayed the country were handed to the judiciary... some were sentenced to death and some to long-term imprisonment."
Such announcements are not unusual in Iran, but the timing has raised concerns that Tehran is hardening its position in its standoff with Western powers.
US Secretary of State Mike Pompeo has also shut down the claims.
"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," Mr Pompeo said in an interview with Fox News Channel.
Iran's supreme leader Ayatollah Ali Khamenei. Source: ABACA
Mr Pompeo declined to comment about any specific cases, but added: "There's a long list of Americans that we are working to get home from the Islamic Republic of Iran."
In recent weeks, the United States has blamed Iran for a string of incidents in the Strait of Hormuz, an important shipping alley in the oil trade bordering one coast of Iran. Iran has denied the accusations.
On Friday, Iran seized a British-flagged oil tanker in the strait. Tehran had previously warned it would retaliate after Britain captured an Iranian tanker off the coast of Gibraltar.
Asked about any possible US role in the tensions, Mr Pompeo said, "The responsibility ... falls to the United Kingdom to take care of their ships."
