The diplomats say International Atomic Energy Agency inspectors visited the nearly finished Arak heavy water reactor last week after a yearlong ban. Separately, they say Iran agreed last week to IAEA requests to expand its monitoring of the Arak uranium enrichment site. It produces material for nuclear fuel that can be further enriched to provide fissile material for warheads.
The diplomats demanded anonymity Thursday because their information was confidential.
A senior Iranian official denied on Tuesday he had made any statement saying Tehran was ready for talks with the West on its disputed nuclear program, state television reported.
The same television network earlier said the official, Iran's envoy to the UN nuclear watchdog, Ali Asghar Soltanieh, "announced Iran's readiness to take part in any negotiations with the West based on mutual respect."
Israeli Ambassador to Washington Michael Oren said Sunday Israel was not mulling a military strike in Iran. In an interview to CNN's Fareed Zakaria, Oren was asked to refer to American estimates Israel would attack the Islamic Republic by the end of 2009.
"I don't think it's true," Oren told Zakaria. "I think that we are far from even contemplating such things right now."