The United States warned yesterday that Iran’s decision to triple its capacity to purify uranium and to move the process to a secretive plant was “provocative” and asked Teheran to reconsider.

Iran earlier said it would transfer its operation to enrich uranium to 20 per cent purity from its Natanz plant to the Fordo underground site near the holy city of Qom, and said it would triple production capacity.

“We are concerned with Iran’s announced intention to continue expanding its enrichment program in violation of Iran’s international obligations,” said National Security Council spokesman Tommy Vietor.

“This decision would involve Iran’s stockpiling of even more near-20 per cent enriched ­uranium without a credible use for this material in the near term.

“Provocative steps such as this do not build confidence in either Iran’s interest in meaningful talks or Iran’s nuclear intent.

“We urge Iran to reconsider this decision, to comply with its international obligations without further delay.”