The International Atomic Energy Agency is trying to probe Iran for purportedly trying to develop such weapons. It has implicated a “foreign expert” in a report as helping Iran work on setting off a nuclear explosion through an explosives trigger.

Diplomats and media have identified him as Vyacheslav Danilenko. They say he has told the IAEA he was not involved in developing such a device.

But diplomats tell The Associated Press Danilenko’s son-in-law has told the IAEA the scientist helped Iran build a related project. That, they say, was a large chamber to contain the force of the blast set off by such testing.