The United States set a March deadline on Thursday for Iran to start cooperating in substance with a U.N. nuclear agency investigation, saying it would otherwise urge reporting the issue to the U.N. Security Council.
Comments by U.S. diplomat Robert Wood to the governing board of the International Atomic Energy Agency signalled Washington's growing frustration at a lack of results in the IAEA's inquiry into possible military dimensions to Tehran's nuclear programme. Iran says the programme has only peaceful goals.
"If by March Iran has not begun substantive cooperation with the IAEA, the United States ... would urge the board to consider reporting this lack of progress to the U.N. Security Council," Wood said, according to a copy of his statement.
"Iran cannot be allowed to indefinitely ignore its obligations ... Iran must act now, in substance," Wood said.
IAEA chief Yukiya Amano earlier on Thursday said the U.N. agency had made no progress in a year-long push to find out if Iran worked on developing an atomic bomb.