TEHERAN - Iranian authorities said on Monday that security agencies had arrested 17 suspects and sentenced some of them to death after dismantling a CIA spy ring in a case announced last month.

The agencies "successfully dismantled a (CIA) spy network", the head of counterintelligence at the Iranian intelligence ministry, whose identity was not revealed, told reporters in Teheran. "Those who deliberately betrayed the country were handed to the judiciary, ... some were sentenced to death and some to long-term imprisonment."

The announcement came as Iran-US tensions soar after the United States withdrew unilaterally from a landmark 2015 nuclear deal and reimposed economic sanctions on the Islamic republic.

The suspects had been "employed at sensitive and crucial centers and also the private sector related to them, working as contractors or consultants", said the official.

Seventeen suspects had been identified, all of them Iranians who had acted independently of each other, he said.

Some of them had been recruited by falling into a "visa trap" set by the US Central Intelligence Agency for Iranians seeking to travel to the US.

"Some were approached when they were applying for a visa, while others had visas from before and were pressured by the CIA in order to renew them," said the official.

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," Iranian state news agency IRNA reported at the time, quoting an intelligence ministry official.

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

Meanwhile, British Prime Minister Theresa May is scheduled to chair an emergency security session on Monday to discuss how to respond to Iran's seizure of a British-flagged tanker in the Strait of Hormuz. British Foreign Secretary Jeremy Hunt is also expected to brief Parliament on the Friday seizure of the Stena Impero tanker, now in a heavily guarded Iranian port.

Britain is considering several options to raise the economic and diplomatic pressure on Iran, but officials said military operations are not being considered at the moment. Britain is also seeking support from key European allies in an effort to keep the Strait of Hormuz open to shipping.

Agencies