Is Iranian bomb research 'mea culpa' needed for nuclear accord?

VIENNA (Reuters) - U.N. watchdog findings that Iran may have worked on designing an atomic bomb helped the West tighten sanctions on Tehran which ultimately forced it, U.S. officials say, to enter serious talks on reining in its nuclear programme.

But as Iran and six world powers enter a crucial stage in their efforts to hammer out a long-term deal by late July, the issue of how to handle suspicions that the Islamic Republic has carried out nuclear weapon research could emerge as a serious stumbling block.