(Bloomberg) -- Iran is nearing a new atomic crisis after failing to cooperate with international inspectors investigating radioactive samples discovered at a site identified by Israel.

The International Atomic Energy Agency’s top inspector, Massimo Aparo, told diplomats in a closed-door meeting in Vienna on Wednesday that Iran is evading attempts to discover the source of man-made and natural uranium particles detected at a warehouse in Tehran earlier this year, according to two officials familiar with the briefing who asked not to be identified.

IAEA acting Director General Cornel Feruta is convening an extraordinary meeting of the 35-member board of governors Thursday to discuss the new concerns. The Romanian diplomat said only last month that Iran had taken “a step in the right direction” in attempting to clarify matters troubling inspectors.

The findings threaten to open a new front in the tense confrontation that has erupted over Iran’s nuclear program since the U.S. withdrew from the multi-power nuclear deal with Tehran last year and reimposed punishing economic sanctions. Iran this week announced it would begin enriching uranium at Fordow, a fortified site built into the side of a mountain.

The IAEA has satellite images showing that the Turquz-Abad site where the particles were found was cleared out after Israeli Prime Minister Benjamin Netanyahu presented documents that Mossad spies smuggled out of a secret warehouse in Tehran. Those files allegedly show Iran lied about a weapons project that operated until 2003, and then intensified efforts to hide its atomic archive after agreeing to the 2015 nuclear accord.

The U.S. is expected to press European allies that remain committed to the pact to support authorizing IAEA inspectors to broaden their investigation, according to the diplomats. That effort would be led by Argentina’s Rafael Grossi, who’ll replace Feruta as director general next month.

The suggestion that Iran could be providing incomplete information has potentially serious consequences. The entire international apparatus of rules that the IAEA enforces is based on verifying the correctness and completeness of nations’ declared nuclear material and nuclear-related activities.

The IAEA’s board referred Iran to the United Nations Security Council in 2006 for failing to fulfill safeguards obligations. The council then imposed crippling international sanctions that were only lifted after the 2015 agreement was agreed.

To contact the reporter on this story: Jonathan Tirone in Vienna at jtirone@bloomberg.net

To contact the editors responsible for this story: Reed Landberg at landberg@bloomberg.net, ;Riad Hamade at rhamade@bloomberg.net, Amy Teibel, Mark Williams

©2019 Bloomberg L.P.