WASHINGTON: The Trump administration on Wednesday extended waivers allowing foreign firms to work at Iranian nuclear facilities without US penalties even as it hit Iran's foreign minister with sanctions.

In a notice sent to Congress, the State Department said it had extended for 90 days waivers that permit European, Russian and Chinese companies to conduct civilian-nuclear cooperation at several Iranian sites. The waivers, which were due to expire on Thursday, had been the subject of heated internal debate with Iran hawks opposed to their extension but others arguing that more time was needed to allow companies to wind down their operations.

The State Department announced the decision in a statement that sought to portray the step as an extension of restrictions on civilian-nuclear cooperation rather than a renewal of sanctions waivers that allow the work in the first place.

"The action today will help preserve oversight of Iran's civil nuclear program, reduce proliferation risks, constrain Iran's ability to shorten its 'breakout time' to a nuclear weapon, and prevent the regime from reconstituting sites," spokeswoman Morgan Ortagus said.

The waivers are the last remaining elements that the US still recognizes from the 2015 Iran nuclear deal from which President Donald Trump withdrew last year.

At the same time, the administration announced that it had imposed financial sanctions on Iranian Foreign Minister Mohammad Javad Zarif as part of its escalating campaign of pressure against the Islamic Republic. The highly unusual action of penalizing the top diplomat of another nation comes a month after Trump signed an executive order placing sanctions on Iran's supreme leader, Ayatollah Ali Khamenei.

Those sanctions are largely symbolic as US officials said Zarif's travels to New York for official UN business will not be inhibited, in accordance with America's international obligations, and the fact that he has little financial interest in American jurisdictions.

In response to that announcement, Zarif tweeted, "It has no effect on me or my family, as I have no property or interests outside of Iran."

Shortly after the Zarif sanctions were announced, the administration notified Congress that it had decided to renew the civilian-nuclear cooperation waivers in the national security interest of the country. Ending the waivers would have been the next logical step in the maximum pressure campaign against Iran and it was favoured by Trump's allies in Congress. But it would have also escalated tensions with Iran and some European allies as fears of conflict in the Persian Gulf grow.

In its notification to Congress, a copy of which was obtained by The Associated Press, the State Department said that extending the waivers would "continue to serve both our Iran strategy and broader non-proliferation goals by constraining Tehran's nuclear capabilities for as long as possible while we work toward a new deal that addresses the totality of Iran's malign behaviour."

Yet, deal critics, including Republican Senators Ted Cruz of Texas and Tom Cotton of Arkansas, said the waivers should be revoked because they give Iran access to technology that could be used for weapons. In particular, they targeted a waiver that allows conversion work at the once-secret Fordow site. The other facilities are the Bushehr nuclear power station, the Arak heavy water plant and the Tehran Research Reactor.

Deal supporters said the waivers give international experts a valuable window into Iran's atomic program that might otherwise not exist. They also say some of the work, particularly on nuclear isotopes that can be used in medicine at the Tehran reactor, is humanitarian in nature.