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President Barack Obama Thursday said Washington and its partners were now working on a package of steps to show Iran the consequences of its decision to snub a nuclear deal with the West.
Obama significantly upped pressure on Tehran, after it rejected UN-backed efforts to send most of its stocks of low-enriched uranium abroad, escalating a showdown with the West over its nuclear program.
In his first public comment on Iran's announcement on Wednesday, Obama said after talks with South Korean President Lee Myung-Bak that Washington and its partners had now begun discussing "consequences" of Iran's decision.
"Our expectations are that over the next several weeks we will be developing a package of potential steps that we could take that will indicate our seriousness to Iran," Obama said.
World powers have warned Iran that it could face tough new sanctions if it rejects the deal, amid sharp concern over what the West say is a plan to develop nuclear weapons.
He bemoaned that Tehran had not been able to agree to the proposed deal, saying he believed internal political factors in Tehran may be to blame, but left the door open for an 11th hour change of heart from the Islamic Republic.
The Obama administration was initially optimistic that Iran would accept the International Atomic Energy Agency (IAEA) deal which emerged from talks between Iran and Russia, China, the United States, Britain, France and Germany.
But hopes had been all but dashed following Iran's slow response and its statement on Wednesday.
Iranian Foreign Minister Manouchehr Mottaki said that Iran had ruled out proposals backed by the major powers for it to ship out more than 70 percent of its uranium stocks before receiving any nuclear fuel in return.
Mottaki said Iran was prepared to consider the idea of a simultaneous exchange of uranium for fuel but the UN nuclear watchdog has already said that idea is unacceptable to the Western powers.
"We will definitely not send out our 3.5 percent enriched uranium," Mottaki said.
Western leaders have expressed fears that Iran might covertly divert some of its uranium stocks and enrich them further to the much higher levels of purity required to make an atomic bomb, an ambition Iranian officials strongly deny.
Western governments support the UN-brokered deal because they believe it would leave Iran with insufficient stocks of low-enriched uranium with which to make a bomb.
Obama's comments stiffened the US line, after the State Department had earlier said that the international community was "not quite" at the point of switching from engaging Iran to pressuring it over its nuclear programme.
France, which had been set to play a central role in the proposed deal, said it would continue to speak with Iran but voiced disappointment at the "negative" stance so far.
"There is a clear and negative response from the Iranians," Foreign Minister Bernard Kouchner said.
Under the IAEA-brokered proposals, Iran would send out 1,200 kilogrammes (more than 2,640 pounds), which would then be further enriched by Russia and converted into fuel by France before being supplied to the Tehran reactor.
"The amount they mentioned for the swap is not acceptable ... and our experts are still studying it," the Iranian foreign minister said.
