The White House Saturday said Iran was "standing in its own way" by imposing an ultimatum on world powers to accept its version of a deal to defuse the building nuclear showdown, AFP reported.
National Security Council spokesman Mike Hammer shrugged off Iran's demand, saying that an existing International Atomic Energy Agency (IAEA) proposal already offered to Tehran was sufficient.
"The IAEA has a balanced proposal on the table that would fulfill Iran's own request for fuel, and has the backing of the international community," Hammer said.
"If getting access to fuel is Iran's objective, then there is absolutely no reason why the existing proposal, which Iran accepted in principle at Geneva, is insufficient. The Iranian government is standing in its own way."
The UN nuclear watchdog had proposed Iran ship most of its low-enriched uranium to Russia and France for processing into fuel for a research reactor.
Tehran rejected a December 31 deadline to accept this, risking new UN sanctions.
But it said on Tuesday it was ready to swap its low-enriched uranium for nuclear fuel abroad, while insisting the exchange happen in stages.