The U.N. chief nuclear inspector says a two-day visit to Iran has ended with his team unable to visit a key military site and without an agreement with Tehran on the way forward.

The International Atomic Energy Agency's Herman Nackaerts spoke Wednesday in Vienna after returning from what the IAEA called "disappointing" talks with Iranian officials.

"We tried to reach agreement on a way forward to resolve all the outstanding issues, and in particular we discussed the possible military dimensions of Iran's nuclear program," said Nackaerts. "We also tried to get access to a site that is relevant for our investigations. So we approached this trip in a constructive spirit, unfortunately we could not get agreement on either of them. So we could not get access, we could not finalize a way forward."