The US will end waivers allowing Russian, Chinese and European companies to continue work at certain Iranian nuclear sites without sanctions, Secretary of State Mike Pompeo said on Wednesday.
The Trump administration will end the waivers it repeatedly renewed since leaving the nuclear deal between Tehran and world powers, known as the JCPOA, in May 2018, Mr Pompeo said on Twitter.
"Today, I am ending the sanctions waiver for JCPOA-related projects in Iran, effective in 60 days," he said.
"Iran’s continued nuclear escalation makes clear this co-operation must end. Further attempts at nuclear extortion will only bring greater pressure on the regime."
By the end of this week, all of the waivers except one will not be renewed.
Mr Pompeo also announced that two Iranian officials, Majid Aghai and Amjad Sazgar, were to be designated by the US for contributing to the proliferation of weapons of mass destruction.
Mr Sazgar is managing director of the Atomic Energy Organisation of Iran's entity responsible for the industrial-scale production of uranium enrichment gas centrifuges.
Mr Aghai is a manager in the organisation's subsidiary that is responsible for research and development of advanced centrifuges.
The waivers due to expire involve: Iran’s Arak heavy water research reactor; providing enriched uranium for the Tehran research reactor; and the transfer of spent and scrap reactor fuel out of Iran.
One waiver covering Iran’s Bushehr nuclear power plant will be extended for 90 days, "to ensure safety of operations".
Mr Pompeo said the foreign companies involved would be given 60 days to wind down operations, after which they would face US sanctions.
"The Iranian regime has continued its nuclear brinkmanship by expanding proliferation sensitive activities," he said.
"These escalatory actions are unacceptable and I cannot justify renewing the waiver.
"The regime’s nuclear extortion will lead to increased pressure on Iran and further isolate the regime from the international community.
"Iran’s nuclear personnel need to make a choice: work for Iranian proliferation organisations and risk being sanctioned, or put their skills to work for the Iranian people in pursuits outside of the proliferation realm."
An internal memo showed Mr Pompeo pushed against extending the waivers but US Treasury Secretary Steve Mnuchin advocated a less hawkish line, The Washington Post reported
Critics of the waivers decision fear it will help Iran to speed up uranium enrichment and prevent any foreign access to the nuclear sites.
Mr Pompeo and other hawks in Congress fear the waivers could gave Iran access to technology from these companies for weaponry use.
The waivers cancellation is another blow to the nuclear deal and sets limits on outside companies operating in Iran.