Iran will expel UN nuclear watchdog inspectors unless US sanctions are lifted by a February 21 deadline set by the hardline-dominated parliament, a lawmaker said on Saturday.

Parliament passed a law in November that obliges the government to halt inspections of its nuclear sites by the International Atomic Energy Agency and step up uranium enrichment beyond the limit set under Tehran's 2015 nuclear deal if sanctions are not eased.

Iran's Guardian Council watchdog body approved the law on December 2 and the government has said it will implement it.

"According to the law, if the Americans do not lift financial, banking and oil sanctions by February 21, we will definitely expel the IAEA inspectors from the country and will definitely end the voluntary implementation of the Additional Protocol," said parliamentarian Ahmad Amirabadi Farahani.

The comments, referring to texts governing the IAEA's mission and activities, were carried by several Iranian media outlets.

In a statement, US Secretary of State Mike Pompeo said Iran had an obligation to allow the inspectors access.

"Once again the Iranian regime is using its nuclear programme to extort the international community and threaten regional security," Pompeo said.

Iran said on Monday it had resumed 20% uranium enrichment at an underground nuclear facility, breaching the nuclear pact with major powers and possibly complicating efforts by US President-elect Joe Biden to rejoin the deal.

Iran began violating the accord in 2019 in response to President Donald Trump's withdrawal of the US from it in 2018 and the reimposition of US sanctions that had been lifted under the deal. Tehran often says it can quickly reverse its breaches if Washington's sanctions are removed.