The head of International Atomic Energy Agency says Iran has invited the agency to visit Arak’s heavy-water plant on December 8, taking a concrete step to ease concerns about its nuclear program.

Iran reached a preliminary agreement with the 5+1 on Sunday, and the UN nuclear watchdog is now examining how the agreement will be “put into practice,” said Yukiya Amano, the IAEA director general, according to Reuters.

The IAEA is to expand its monitoring of Iran’s nuclear facilities, and Amano said the detailed analysis of how the IAEA will approach this task will take some time, as it will have to look at the “implications of funding and staffing.”

The December 8 visit is part of a deal signed earlier this month between Iran and the IAEA.

According to Iranian foreign minister: “Capacity at the Arak site is not going to increase. It means no new nuclear fuel will be produced and no new installations will be installed, but construction will continue there.”

The U.S. has also said that Iran could continue with some construction at the Arak nuclear plant as long as it refrains from nuclear activities banned in the Geneva deal.