The official said the pictures "reinforce what Israel has been saying all along ... the Iranian nuclear program is not benign." He spoke on condition of anonymity pending a formal government response.
On Wednesday, pictures provided by unspecified member countries to the International Atomic Energy Agency - the UN nuclear agency - appear to show trucks and earth-moving vehicles at Iran's Parchin military site. Diplomats said the images suggested the trucks could be carting away radioactive material created in nuclear testing.
Iran says its nuclear program is solely for peaceful purpose - a claim Israel and the West reject.
Earlier Thursday, Yukiya Amano, the head of the International Atomic Energy Agency, told CNN that Iran is not telling us everything about its nuclear program.
"We have the indication or information that Iran has engaged in activities relevant to the development of nuclear explosive devices," Yukiya Amano told CNN.
Iran faces growing international pressure over its nuclear program, which it insists is peaceful. Israel has hinted that it might resort to a pre-emptive military strike to stop Tehran's program.
The diplomatic account came only a day after the ISNA news agency reported that Iran indicated that it would give the UN nuclear watchdog access to the Parchin complex.
An International Atomic Energy Agency report last year said that Iran had built a large containment chamber at Parchin, southeast of Tehran, to conduct explosives tests that are "strong indicators" of efforts to develop an atom bomb.