The images of the Parchin Iranian military complex, located about 20 miles southeast of Tehran, show trucks and earth-moving vehicles doing cleanup, two diplomats told CNN.
It was not clear what the vehicles were cleaning, the diplomats said.
But the images raised concerns inside the International Atomic Energy Agency -- the United Nations' nuclear watchdog -- that Iran was attempting to remove any evidence linking Parchin to nuclear-weapons development, CNN and The Wall Street Journal reported.
The IAEA twice tried to visit Parchin last month to assess its suspicions Iran conducted explosives tests there with the aim of developing atomic weapons.
Tehran rejected the IAEA's requests twice.
But senior Iranian officials said Tuesday Tehran was now reassessing the request and would likely allow a visit in the coming months, the IAEA said.
The reassessment is considered evidence Iran is trying to clean up Parchin before letting the IAEA inspectors visit, the diplomats told CNN.
Iran insists its nuclear program is for peaceful civilian uses only.
IAEA Director General Yukiya Amano hinted at concerns over Parchin earlier this week when he told a gathering of the agency's board of governors in Vienna there was disturbing activity at the site.
Western diplomats first thought Amano was referring to nuclear-weapons work, the Journal reported. But they later realized he was referring to Iranian attempts to cleanse the site.
Amano told CNN his agency -- which reports to the U.N. General Assembly and Security Council -- has "the indication or information that Iran has engaged in activities relevant to the development of nuclear explosive devices."
"Iran is not telling us everything," he said.
The five permanent Security Council members plus Germany planned to issue a joint statement Thursday underscoring their "concerns about Iran's nuclear activities, including its uranium-enrichment activities," a Western diplomat told CNN.
The hope of the statement by the United States, France, Britain, China, Russia and Germany "is it helps isolate Iran and indicates that Russia and China are in the West's camp in calling on Iran to comply," the diplomat said.
The six powers agreed Tuesday to resume nuclear talks with Iran that were stalled for more than a year.