A senior Obama administration official told Congress Thursday that Iran has begun removing thousands of centrifuges and is shipping low-enriched uranium out of the country under the terms of the international nuclear agreement, but his testimony did not allay senators' fears that Tehran intends to cheat on the deal.

Stephen Mull, the lead coordinator for implementation of the deal at the State Department, said Iran has begun dismantling its uranium enrichment system by removing thousands of centrifuges and transferring them into a storage facility that will be monitored by international nuclear inspectors.

"It has already removed more than 5,000 of its machines and is likely to move quickly to remove the rest in the coming days," Mull told the Senate Foreign Relations Committee.

He said Iran also is reducing its stockpile of various forms of enriched uranium to no more than 300 kilograms of material enriched up to 3.67 percent.

"It will accomplish this primarily by shipping a significant amount of such material outside Iran, while also diluting the remaining excess to the level of natural uranium or below," Mull said. "Commercial contracts are in place for Iran to ship its enriched uranium stockpiles to Russia. We expect that this material — approximately 25,000 pounds of material enriched up to 20 percent low-enriched uranium — could leave Iran in the coming weeks."

Republican and Democratic members of the committee, however, expressed concern about recent actions taken by Iran, which they fear foreshadow Iranian noncompliance with the nuclear deal.

Saying that the deal is off to a "terrible start," Sen. Bob Corker, R-Tenn., chairman of the committee, rattled off a list of recent actions by Iran, including the conviction of Jason Rezaian, a reporter for The Washington Post; the export of weapons to Syria and Yemen; and the violation of the U.N. ballistic missile test ban.

"Can anyone here point to any substantive consequences that Iran has faced?" Corker said. "We see no evidence of them paying a price for any of these actions."

Sen. Kelly Ayotte, R-N.H., and 35 GOP senators wrote President Barack Obama on Thursday noting the ballistic missile test.

On Oct. 10, Iran conducted a ballistic missile test that, according to Samantha Power, the U.S. representative to the U.N., violated Security Council resolution 1929. Following that test, Ayotte and Sen. Mark Kirk, R-Ill., sent a letter on Oct. 14 urging the administration to respond and warning that "tough statements followed by inaction will further undermine U.S. national security."

On Thursday, Ayotte and the other senators wrote, "This approach toward Tehran undermines further an already weak Iran deal and jeopardizes our national security interests and the safety of Americans and our allies."

Democratic senators at the committee agreed that there should be "zero tolerance" of violations of the nuclear deal or any other international obligations, said Sen. Ben Cardin of Maryland, the senior Democrat on the committee. His comments were echoed by Democratic Sens. Tim Kaine of Virginia and Chris Coons of Delaware.