IAEA Director General Yukiya Amano will arrive in Tehran on Sunday. Reuters

Iran is getting a visit from the United Nations' nuclear agency on Sunday, a surprise development as Iran prepares for scheduled talks with Western powers next week.

Yukiya Amano, director general of the International Atomic Energy Agency, or IAEA, and his top aides will be traveling to Tehran to “discuss issues of mutual interest with high Iranian officials,” the agency said. Amano will become the first IAEA director general to visit Iran since his predecessor, Mohamed ElBaradei, did in 2009.

Last fall, Tehran was extremely critical of Amano after the IAEA reported that Iran had been working to develop nuclear weapons. State-run news agency Press TV accused him of being an agent of U.S. interests and blasted the report as a fiction designed by the West to justify a military strike on Iran.

Tensions between the U.S. and Iran, as well as between the U.N. and Iran, have somewhat cooled down since then, and nuclear talks with the so-called P-5 Plus 1 group -- Britain, China, France, Russia, and the U.S., plus Germany -- have restarted. The next meeting between the two sides is scheduled to take place in Baghdad on Wednesday.

During the visit this weekend, Amano is expected to try getting Iran to agree to terms for giving IAEA inspectors access to nuclear sites and related documents, according to the Jerusalem Post.

There are still some outstanding issues, but there is a possibility an agreement is reached on Monday, one Western diplomat told Reuters, saying it would be a step forward on the process side.

A meeting between Iranian and IAEA officials in Vienna on Monday has been canceled.