Iran resumed uranium enrichment at its underground Fordow plant south of Tehran Thursday in the latest step back from commitments under a landmark 2015 nuclear deal.

"Iran continues to conceal its nuclear programme," Netanyahu said in a statement on his country's arch-foe.

"Iran also continues uranium enrichment, whose sole purpose is the production of nuclear weapons. I urge the international community to wake up."

A US official said Thursday testing by the United Nations nuclear watchdog confirmed uranium traces at a separate warehouse Netanyahu spoke of during an address to the UN General Assembly in 2018.

Iran ridiculed the claim at the time and has always said its nuclear activity is for civilian purposes only.

Diplomatic sources in Vienna say the UN's International Atomic Energy Agency took samples from the site in the Turquzabad district of Tehran in the spring.

The Iranians' responses to the IAEA have not resolved all of the agency's questions, the sources said.

A European diplomatic source on Thursday said radioactive material was detected at the site and could have been stored there while in transit to another hitherto concealed facility south of the city of Isfahan.

"Efforts are being to made to gain access" to this second site, the source said.

Israeli security and intelligence officials, speaking on condition of anonymity, say the warehouse held nuclear material and equipment from 2009 to 2018, when -- these sources say -- Iran decontaminated the site.

They allege the undeclared site amounts to a violation of the Non-Proliferation Treaty against the spread of nuclear weapons.

They also argue it points to other undeclared sites, contending the material must have been moved elsewhere and the uranium processed at a separate location.

Israel opposed the 2015 nuclear deal and urged US President Donald Trump to withdraw from it, which he eventually did, arguing it does not do enough to prevent Tehran from eventually obtaining nuclear weapons.

Netanyahu also argues the lifting of sanctions as per the deal allowed Iran to finance proxy militant groups in the Middle East.

But at the time when Trump withdrew from the deal in 2018, most world powers said the accord was working as intended and was the best way to keep Iran from acquiring a nuclear weapons capability.

In April 2018, Netanyahu said in a live television address that Israel had obtained a trove of nuclear files from Iran in an intelligence operation.

He said they spelt out "proof" of an Iranian nuclear weapons plan that could be activated at any time.

But while he accused Iran of lying about its nuclear ambitions, he did not provide evidence that it had actively worked to obtain an atomic weapon since the 2015 nuclear accord.