The New York Times says international inspectors are requesting access to two secret Iranian military sites, where intelligence suggests Tehran could be developing nuclear weapons.
The newspaper says inspectors from the International Atomic Energy Agency have seen satellite photographs that indicate high explosives are being tested.
According to the Times, several sources, including IAEA member countries, diplomats and weapons experts provided intelligence about the Iranian military sites.
This week, Iran agreed to suspend uranium enrichment activities, staving off a U.S. push to bring the matter to the U.N. Security Council for possible sanctions over Tehran's alleged nuclear weapons program.
But the Iranian government says it has not abandoned its right to enrich uranium.
Some information for this report provided by Reuters.