The commercial imagery shows that Iran has moved heavy construction equipment to the area. But the senior intelligence official, who is familiar with the imagery in question, said the U.S. is confident that such sanitization efforts cannot succeed because radioactive materials, if present, are extremely difficult to conceal.
"The (International Atomic Energy Agency) is familiar with sanitization efforts and the international community has confidence in the IAEA's technical expertise," the official said.
Bloomberg first reported the satellite imagery at Parchin.
Sen. Chris Coons, D-Delaware, told reporters on Tuesday that he has "concerns about the vigorous efforts by Iran to sanitize Parchin."
However, he indicated his concerns were not a deal breaker.
"I've gotten some reassurance about how difficult it is for them to effectively conceal what we know to have been their illicit nuclear weapons developments there," he said.
He added that his bigger worries are about how the IAEA would operate once the Iran nuclear agreement is in place.
"What I'm most concerned about going forward is the integrity of the IAEA process: whether they question Iranian scientists, whether they actually have a meaningful inspection at the site of Parchin is more relevant than what they are going to learn. We know what the Iranians did at Parchin," Coons said.
New Hampshire Democratic Sen. Jeanne Shaheen told reporters that she asked IAEA Director Yukiya Amano at a Senate Foreign Relations Committee briefing on Wednesday what Parchin might be used for and said his answer helped clarify the situation.
"It is not a place where they are manufacturing a nuclear bomb," Shaheen said.
After the briefing with Amano, Democratic Sen. Chris Murphy said he has confidence the inspections team will give us "our best chance of catching Iran at Parchin."
"Not (that) this regime nor any can be 100% foolproof, but this is the best chance that we'll have," he added.
Murphy said many senators in the meeting made it clear that they wanted to read the IAEA deal with Iran, but added, "It would be a complete violation of everything -- the foundation of the IAEA's protocol with nations -- for them to make the details of this agreement public, so I think yeah, people were frustrated with that."
A furious lobbying effort by both supporters and foes of the Iran nuclear deal continues in the Senate ahead of a mid-September vote on the agreement. On Wednesday, Senate Majority Leader Mitch McConnell said the Iran debate will begin on the Senate floor on Sept. 8 after the August recess is over.
Coons has said he still has concerns about the agreement and is reviewing the deal. Murphy announced in a floor speech on Wednesday that he supports the deal, while Shaheen hasn't yet revealed her position.