U.S. Secretary of State Mike Pompeo said on Monday that Washington does not want war with Iran.
Regarding the British tanker incident, Pompeo added that it falls on the UK to take care of their ships.
Iran made the announcement in state media, saying spies had been arrested in the 12 months to March 2019. 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.
"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," Pompeo said in an interview with Fox News Channel.
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.