Iran arrested 17 suspects and sentenced some to death after dismantling a US CIA spy ring, an official said Monday, as tensions soar between the Islamic republic and arch-enemy the US.

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."

The suspects were arrested between March 2018 and March 2019.

Tehran has been at loggerheads with Washington and its allies since May 2018, when President Donald Trump unilaterally withdrew the US from a landmark 2015 deal putting curbs on Iran's nuclear program in exchange for sanctions relief.

The US administration reimposed biting sanctions on Iran, which retaliated by increasing its enrichment of uranium beyond limits set in the nuclear accord.

Trump called off air strikes against Iran at the last minute in June after the Islamic republic downed a US drone, one of a string of incidents including attacks on tankers in the Gulf.

The tensions have escalated since British authorities seized an Iranian oil tanker in July on suspicions it was shipping oil to Syria in breach of EU sanctions.

In what was seen by Britain as a tit-for-tat move, Iran's Revolutionary Guards seized a UK-flagged tanker in the strategic Strait of Hormuz on Friday, angering the US ally.

Iran said last month that it dismantled a spy network linked to the CIA.

"Following clues in the American intelligence services, we recently found the new recruits Americans had hired and dismantled a new network," state news agency IRNA reported at the time, quoting an intelligence ministry official.

IRNA said Iran had carried out the operation in cooperation with "foreign allies," without naming any state.