Obama: Iran must take concrete action

WASHINGTON (Reuters) - U.S. President Barack Obama said on Thursday talks between Iran and world powers had been a "constructive beginning" but Tehran must now take concrete steps to come clean on its nuclear program or else face additional pressure.

"The Iranian government heard a clear and unified message from the international community in Geneva," Obama said at the White House after negotiations in Geneva wrapped up.

"Iran must demonstrate through concrete steps that it will live up to its responsibilities with respect to its nuclear program."

Obama insisted that Tehran must meet its pledge to allow immediate international inspections of a second nuclear fuel site disclosed last week.

"It must grant unfettered access to IAEA inspectors within two weeks," he said.

Obama and other Western leaders have threatened further sanctions if Tehran fails to comply with international demands.

Using a carrot and stick approach, Obama said, "We've made it clear that we will do our part to engage the Iranian government on the basis of mutual interest and mutual respect but our patience is not unlimited."

He said Iran must prove that its nuclear program is for peaceful purposes, as it maintains, and not for developing nuclear weapons as Western nations allege.

"We expect to see swift action. We're committed to serious ... engagement but we're not interested in talking for the sake of talking," Obama said.

"If Iran does not take steps in the near future to live up to its obligations, then the United States will not continue to negotiate indefinitely and we are prepared to move toward increased pressure," he said.

"This is a constructive beginning but hard work lies ahead," he said.

Obama also said he backed an IAEA proposal, which he said was agreed to in principle by Tehran, for Iran to transfer low-enriched uranium to a third country for fuel fabrication, a step he called a confidence-building step.

Such a move would reassure Western countries that Iran is not enriching uranium to make a nuclear bomb.