— After keeping away inspectors for two years, Iran is inviting the U.N. nuclear agency to a facility linked to an unfinished reactor that could produce enough plutonium for up to two warheads a year.

Announcing the invitation Thursday, Yukiya Amano, who heads the U.N.’s International Atomic Energy Agency, said the IAEA will accept the offer to visit the heavy-water plant in the central city of Arak. His announcement to the agency’s 35-nation board comes less than a week after a landmark nuclear deal between Iran and six world powers.

He also said his agency first learned that it would be tasked with supervising Iranian compliance as the agreement was struck in Geneva over the weekend. Amano didn’t give a date for when the IAEA would start implementing its role under the deal but suggested that it would take some time, in part because his agency wasn’t informed earlier to prepare for the mission.

The invitation for Dec. 8 is not part of the six-power deal, which commits Iran to freeze its nuclear program for six months in return for limited relief from economic sanctions. But it shows that Tehran is starting to comply with separate commitments to open previously off-limits sites to IAEA inspectors.

The status of the Arak plant had been one of the major issues during the negotiations that led to the nuclear agreement.

Iranian Foreign Minister Mohammad Javad Zarif said Wednesday that some construction at Arak will continue. When completed, Arak could produce plutonium that could be used for nuclear weapons. Iran insists that its program is only for peaceful purposes such as producing electricity, and for scientific and medical research.

Iran had scheduled completion for next year, a timetable described by experts as too ambitious.

U.S. State Department spokeswoman Jen Psaki said Zarif’s comments didn’t constitute a violation of the agreement, even though Iran effectively pledged to freeze advancement at the facility.

Iran’s decision to allow inspectors to visit the Arak heavy-water plant will enable inspectors to get a clearer picture of how much material the plant is producing and other technical details.

IAEA employees have had some access to the reactor, which is 150 miles southwest of Tehran. But they haven’t been able to inspect the plant at the site since 2011. Heavy water helps control nuclear activity of the fuel rods used in some types of reactors.

Beyond commitments on the Arak reactor, Iran also agreed under the nuclear deal to limit uranium enrichment. It pledged to stop enriching uranium to a stage that is only a technical step away from the concentration needed to arm nuclear warheads and to keep its stockpile of low-enriched uranium from expanding.

A senior Iranian official said Thursday that Iran would increase its low-level uranium enrichment. Iranian nuclear chief Ali Akhbar Salehi told the official IRNA news agency that centrifuges previously used for higher-level enrichment would now be turned to produce low-enriched uranium.

He didn’t elaborate. But the Geneva deal doesn’t prohibit Iran from making more enriched uranium. It stipulates only that all newly produced material must be turned into oxide, which is difficult to reconvert.

Diplomats told the Associated Press on Wednesday that the agency probably will not be in a position to start on that role until January. While giving no dates, Amano indirectly confirmed some delays, telling the meeting Thursday that implementation will “take some time.”

“I cannot tell you when we will be ready,” Amano later told reporters, saying his agency needed intensive preparation for a “quite complicated task” to do a proper job.

— Associated Press