The chief U.S. envoy to the IAEA, Kenneth Brill, said the results of inspections by the agency's teams in Iran reveal that Iran's claims about the peaceful nature of its nuclear program are not credible.

"I think it is striking that the more the agency learns, the more the Iranians have to change their stories, with comments by the Iranian officials over the past couple of days about the October declaration being the most recent example. We were told before, the board and the world was told, by a number of very senior Iranian officials including those commenting on the issue yesterday and today that that declaration would be full, complete and represent total Iranian transparency," he said. "When it was proved that this was not the case, that the report was neither correct nor complete in very significant ways, as the agency made it clear, they say 'we didn't mean that, we didn't mean it was to be full and complete.'"

This board meeting is expected to pass a tough resolution on Iran this week, but not to refer the matter to the U.N. Security Council. Diplomats say the resolution will be designed to keep the pressure on Iran to come clean on its nuclear program by the next board meeting in June.

But Ambassador Brill said that will likely not be the end of of the IAEA's concerns about Iran. "The fact is that the Iranians change their stories to fit the facts. This board has a lot of work to do and I expect to be dealing with the Iranian issue in many boards to come," he said.

Earlier Monday, IAEA chief Mohamed ElBaradei said he is seriously concerned about Iran's failure to declare sensitive nuclear research and equipment that the inspectors found, which could be used in a weapons program. His report to the board of governors says most of the workshops inspected are owned by Iranian military industrial organizations.

But Iran says its program is for peaceful purposes, and in a written statement circulated to reporters says only three out of ten workshops involved in manufacturing sophisticated centrifuge components belong to the defense industry.