The chief of the IAEA Yukiya Amano said he is not optimistic about talks with Iran next week on getting access to Parchin military complex in Iran, Reuters reported.
Western states suspect Iran of using the complex for atomic-weapons related work.
"The outlook is not bright," Yukiya Amano, director general of the International Atomic Energy Agency, said in Tokyo.
He was referring to talks to be held next week on getting access to the Parchin military base and officials involved in Iran's nuclear programme.
The United States, Israel and some of their allies suspect Iran of pursuing non-civilian objectives in its nuclear energy program.
Iran rejects the allegations, arguing that as a committed signatory to the nuclear Non-Proliferation Treaty (NPT) and a member of the International Atomic Energy Agency (IAEA), it has the right to use nuclear technology for peaceful purposes.
In addition, the IAEA has conducted numerous inspections of Iran's nuclear facilities but has never found any evidence showing that Iran's civilian nuclear program has been diverted to nuclear weapons production.