The head of the United Nations atomic watchdog agency left Iran late Tuesday after failing to reach a deal to allow inspectors access to a factory making equipment for Tehran’s nuclear program, diplomats said Wednesday, casting a fresh shadow over international nuclear talks set for next week.

The Wall Street Journal reported last week that the factory, in Karaj, Iran, had resumed producing key parts for centrifuges, which are used to enrich uranium, without any monitoring by the International Atomic Energy Agency. The diplomats said talks between the IAEA and Iran were continuing.

With Iran, the U.S. and other major powers set to resume negotiations in Vienna next Monday aimed at curbing Iran’s nuclear capabilities, that raised new concerns among Western officials that Iran could diverting nuclear equipment to a possible future covert nuclear weapons program.

Iran says its nuclear program is purely peaceful.

IAEA Director-General Rafael Grossi traveled to Tehran on Monday for meetings with senior Iranian officials. He hoped to win access for his inspectors to go to Karaj and restore agency cameras that had been removed after an explosion at the plant in June. Iran has blamed Israel for the blast. Israel has neither confirmed nor denied involvement.

Diplomats said talks between the IAEA and Iran continued overnight and continue to try to reach an agreement which could unlock access to Karaj.

Mr. Grossi is scheduled to give a press conference later Wednesday on the sidelines of the IAEA’s Board of Governors meeting with member states.

The Biden administration has set as one of its top foreign policy goals reviving the 2015 nuclear deal between Iran and six major powers, which placed strict but temporary restrictions on Iran’s nuclear activities in exchange for lifting most international sanctions.

However U.S. officials have warned that time is running out to be able to rebuild the nuclear deal because of Iran’s ongoing nuclear activities. Iran has gradually breached most of the limits in the 2015 deal since former President Donald Trump took the U.S. out of the agreement in May 2018.