Iran nuclear talks stall, even with US at table

In response, the six gave Iran two weeks to respond to their demand, setting the stage for a new round of U.N. 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.

Officials and diplomats refused to characterize the timeframe as an ultimatum, but it appeared clear that Iran now has a de-facto deadline to show flexibility.

EU envoy Javier Solana said that Iran still has to answer a request made on behalf of the five permanent U.N. 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. He said the two-week timeframe was meant to give Iran the space to come up with "the answers that will allow us to continue."

In Washington, a U.S. official was 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," said State Department spokesman Sean McCormack.

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 then an hour after they started. "Suspension--there is no chance for that," he told reporters.