VIENNA, June 15 - Iran has admitted that it conducted small-scale experiments to create plutonium, one of the pathways to building nuclear weapons, for five years beyond the date when it previously insisted it had ended all such work, a senior official of the International Atomic Energy Agency is expected to report Thursday.

In an oral statement to be delivered at a meeting of the nuclear watchdog agency's board, the agency's deputy director, Pierre Goldschmidt, will say Iran made the admissions after being confronted with the result of laboratory tests conducted on samples collected from an Iranian nuclear site...

..."From what I understand of the report, which I haven't seen, it doesn't say as much about a new capability or intention as much as it says about Iran's lack of candor so far," Corey Hinderstein, deputy director of the Institute for Science and International Security, a Washington research organization that has been critical of Iran, said in a telephone interview.

"It shows that Iran has yet to come clean about its nuclear program," Ms. Hinderstein said. "Each new revelation that they haven't told the truth, especially at this late date, increases questions about what else they're hiding."

But an Iranian negotiator interviewed in Vienna, Cyrus Nasseri, denied that the disclosures regarding plutonium experiments indicated any effort by Iran to conceal activities.

"What difference would it make for us to say these tests were made 13 years ago or 10 years ago?" he said. "It would make no difference at all, so there cannot be any motive of concealment." He said the disclosure of new dates reflected the time required to examine the record rather than concealment.

"I can understand that some might want to make a big story out of this," he continued, "but I'm sorry, it's not a big story."...