Iran may be withholding information needed to establish whether it tried to make nuclear arms, the International Atomic Energy Agency said May 26 in an unusually strongly worded report.

The tone of the language suggesting that Tehran continues to stonewall the agency — the U.N. nuclear monitor — revealed a glimpse of the frustration felt by agency investigators stymied in their attempts to gain full answers to suspicious aspects of Iran's past nuclear activities.

Iran has described its cooperation with the agency probe of its alleged nuclear weapons experiments as positive, suggesting it was providing information requested by agency officials. Indirectly disagreeing, the agency said that Iran continued to deny such activities, dismissing evidence to the contrary submitted for its perusal as misleading or false.