The White House on Friday said it could not confirm that Iran had taken new steps on enriching uranium but said Tehran must not develop fissile material that might be used for atomic weapons.
"I don't know that we've got confirmation on the reports, but our position on the Iranian situation is clear: We don't want them moving toward development of fissile material," spokesman Tony Snow told reporters.
Snow's comments came after Iran's ISNA news agency reported that Iranian scientists have begun feeding gas into a second cascade of centrifuges to enrich uranium, defying UN threats of sanctions over Iran's nuclear program.
"The second cascade was set up two weeks ago, and this week gas was injected in them," an unidentified official told the agency. "We have the product of the second cascade."
Iran on Wednesday confirmed it had installed new equipment to step up uranium enrichment and said it would imminently start pumping gas into the equipment.