Iran still stalling as nuclear deadline looms - U.N. agency

International Atomic Energy Agency (IAEA) Director General Yukiya Amano arrives for a board of governors meeting at the IAEA headquarters in Vienna November 20, 2014. REUTERS/Heinz-Peter Bader

VIENNA (Reuters) - Tehran has yet to explain away allegations it conducted atomic bomb research, the head of the U.N. nuclear agency said on Thursday, four days before a deadline for Iran and six world powers to reach a deal on the Iranian nuclear programme.

As U.S. Secretary of State John Kerry flies to Vienna for what are meant to be final talks to clinch a deal with Iran, International Atomic Energy Agency (IAEA) chief Yukiya Amano said he was still unable to provide "credible assurance" Iran had no undeclared nuclear material and activities.