Tehran's nuclear plans are "a matter of serious concern" and require "substantial explanations" from Iranian lofficials," the International Atomic Energy Agency said in a report, The New York Times reported.
The report said Iranian officials have not cooperated with an investigation into whether its nuclear ambitions were for peaceful purposes, as the government of President Mahmoud Ahmadinejad has said.
The nine-page IAEA report says Western intelligence agencies have documents that indicated the Iranians have ventured into explosives, uranium processing and a missile warhead design, which are ordinarily associated with with building nuclear arms.
"There are certain parts of their nuclear program where the military seems to have played a role," said one senior official who spoke on condition of anonymity. "We want to understand why."
The documents cited by the Western intelligence agencies to make their case against Iran are "forged" or "fabricated," Tehran says.
Ali Asghar Soltanieh, Iran's ambassador to the IAEA, said the report vindicated Iran's nuclear activities.
He said another document in the report "shows Iran's entire nuclear activities are peaceful," the Fars News Agency quoted him as saying.