Officials say satellite surveillance has shown a recent increase in activity at an Iranian site suspected of secret work on nuclear weapons.
One tells The Associated Press that it appears Tehran is trying to cover its tracks by removing any evidence of nuclear research and development.
Officials from two other countries confirm increased activity but say they do not have reasons to believe it is linked to such efforts.
Their focus is on a structure believed to be housing a large metal chamber at a military site at Parchin that an International Atomic Energy Agency report earlier this month described as being used for nuclear-related explosives testing.
A senior diplomat said Monday the agency is closely monitoring all suspect sites mentioned in the agency's report. All the officials asked for anonymity because their information is confidential.