The head of the U.N. nuclear agency says he is uncertain whether Iran will agree to allow his agency to restart an investigation into the Islamic Republic's suspected secret nuclear arms program.

International Atomic Energy Agency chief Yukiya Amano said Friday in Tokyo that the likelihood of an agreement at talks this week "remains unclear." IAEA officials have reported some progress after their previous meeting in December, citing a possibility to resume its probe this year following another round of talks Jan. 16.

Amano, expected to stay on the top job at the agency for four more years, is in Japan for talks with its newly elected Prime Minister Shinzo Abe and his government.

Iran denies it is developing nuclear weapons, saying its nuclear program is for peaceful power generation.