(Reuters) - The U.N. nuclear agency chief said on Thursday that Iran had failed to provide explanations in response to allegations of possible atomic bomb research, and he called on Tehran to step up cooperation with a long-running investigation.

"I call upon Iran to increase its cooperation with the agency and to provide timely access to all relevant information, documentation, sites, material and personnel," Yukiya Amano, director general of the International Atomic Energy Agency, told a meeting of the IAEA's 35-nation board of governors.

Iran and six world powers, also meeting in the Austrian capital this week, aim to reach a diplomatic agreement by a Nov. 24 deadline to end a 12-year dispute over the Islamic Republic's atomic activities.