Israel has shared intelligence over the past two weeks with the US and several European allies suggesting that Iran is taking technical steps to prepare to enrich uranium to 90% purity — the level needed to produce a nuclear weapon, two US sources told Axios’ Barak Ravid on Monday.

Enriching to 90% would bring Iran closer than ever to the nuclear threshold. The Israeli warnings come as nuclear talks resume in Vienna, with Iran returning to the negotiating table on Monday after a five-month hiatus.

Enrichment alone will not produce a bomb. Estimates vary as to how long it would take Iran to master the additional technological requirements, but US and Israeli intelligence sources have put the timeline at one to two years.

The intelligence Israel shared with the Biden administration suggests the Iranian preparatory steps would allow Iran to move ahead with 90% enrichment within weeks if it chose to do so, according to one of the US sources cited by Ravid.

Israeli intelligence analysts assess that Iran could take that dramatic step soon in an attempt to gain leverage in the Vienna talks, the source said.

Israel also shared an intelligence assessment that Iran's desire for leverage in Vienna could lead Tehran to further increase attacks against US forces and interests in the region via proxies in Yemen, Syria and Iraq, the US source said.

Asked to comment on this story, a senior Biden administration official declined to discuss intelligence matters but said it was “no secret that the former administration's decision to abandon the 2015 nuclear deal led to a dramatic and unprecedented acceleration of Iran's nuclear program," and that the US was focused on diplomacy with Iran but "prepared to pursue other options should diplomacy fail."

The Israeli Prime Minister’s Office, Foreign Ministry and Ministry of Defense declined to comment.

Iran has gradually scaled back its compliance with the 2015 nuclear deal it signed with world powers in response to former US President Donald Trump’s withdrawal from the agreement in May of 2018.

The Biden administration is trying to get back into the agreement and on Monday, indirect talks between the sides resumed for the first time since June.

Iran has repeatedly demanded that the US lift sanctions imposed on Iran and also reassure Iran it will not abandon the deal again as a precondition for its returning to compliance with the deal.