FILE PHOTO: International Atomic Energy Agency (IAEA) Director General Yukiya Amano waits for the start of a board of governors meeting at the IAEA headquarters in Vienna, Austria June 4, 2018. REUTERS/Leonhard Foeger/File Photo

VIENNA (Reuters) - U.N. nuclear watchdog chief Yukiya Amano returned to work on Tuesday after an unexpectedly long absence following medical treatment that his agency has provided no details of.

The International Atomic Energy Agency posted pictures online of Amano chairing a meeting with staff and being presented with flowers at its headquarters in Vienna. A spokesman confirmed he was back at the headquarters.

The agency, which among other things is in charge of policing the restrictions on Iran’s nuclear activities under Tehran’s 2015 deal with major powers, said in early September that Amano had undergone a medical procedure outside Austria that was successful.

The agency said at the time that Amano, a 71-year-old Japanese diplomat who was reappointed last year to a third four-year term, was expected to return to Vienna in early October.

Although the IAEA said Amano continued to oversee the agency’s work, he was away during one of its busiest times of the year, including last month’s General Conference, an annual gathering of its member states.

He addressed the General Conference in a brief video message in which he appeared thin and weakened.