A US decision to bend policy and sit down with Iran at nuclear talks fizzled today as Tehran stonewalled six world powers on their call for Iran to freeze uranium enrichment.
In response, the six gave Iran two weeks to respond to their demand, setting the stage for a new round of UN sanctions.
Iran's refusal to consider suspending enrichment was an indirect slap at the United States, which had sent Undersecretary of State William Burns to the talks in hopes the first-time American presence would encourage Tehran into making concessions.
Diplomats at the negotiating table refused to characterise the two week timeframe as an ultimatum - but it was clear the offer was a de facto deadline for Tehran to show flexibility.
EU envoy Javier Solana said Iran still has to answer a request made on behalf of the five permanent UN security council members plus Germany to "refrain from any new nuclear activity".
"We have not gotten all the answers to the questions," Solana told reporters after apparently unsuccessful daylong talks.
He said the two weeks should allow Iran to come up with "answers that will allow us to continue."
American officials were blunter.
"We hope the Iranian people understand that their leaders need to make a choice between cooperation, which would bring benefits to all, and confrontation, which can only led to further isolation," State Department spokesman Sean McCormack said in Washington.
In diplomatic terms, "further isolation" is shorthand for economic and political sanctions.
Keyvan Imani, a member of the Iranian delegation, cast doubt over the value of talks less than an hour after they started.
"Suspension - there is no chance for that," he told reporters in the courtyard of Geneva's ornate City Hall, the venue of the negotiations.
Imani also downplayed the presence of Burns - even though the Americans had previously said they would not talk with the Iranians on nuclear issues unless Tehran was ready to stop all enrichment activity.
"He is (just) a member of the delegation," Imani said.
Chief Iranian negotiator Saeed Jalili evaded the issue of suspension, demanded as part of the six power "freeze for freeze" proposal that carries a commitment of no new UN sanctions in exchange for an Iranian pledge to stop expanding its enrichment program.
Instead he spoke in generalities about the need for cooperation and constructive exchanges of ideas that reflected Tehran's reluctance to focus on the six power offer.
"Iran is calling on the Western powers to resume the dialogue," he said.
Iran already is under three sets of UN sanctions for its refusal to suspend enrichment, which can generate both nuclear fuel and the fissile material at the core of nuclear warheads. While Tehran says it has a right to enrich for peaceful purposes, the sanctions reflect international concern that it might use its program to make weapons.
The "freeze for freeze" offer delivered to Iranian officials last month by Solana envisions a six week commitment from Iran to stop expanding enrichment in exchange for a six week moratorium on new sanctions.
That aims to lead to formal negotiations in which the six nations hope they can convince Tehran to indefinitely ban enrichment.
Burns' decision to attend the Geneva talks showed that Washington was willing to temporarily accept the freeze plan - something less than fully mothballing the program as it had always demanded.
Recent Iranian statements had suggested Tehran was looking to improve ties with the United States, with officials speaking positively of deliberations by the US administration to open an informal diplomatic presence in Tehran after closing its embassy decades ago.
Iran and the United States broke off diplomatic relations after the 1979 Islamic Revolution and the hostage crisis at the US Embassy in Tehran. US interests in Iran are now represented by the Swiss Embassy in Tehran.