Diplomatic efforts to end the eight-year-old impasse over Iran's nuclear program ran aground Saturday after Iranian officials refused to bargain with the United States and other world powers at a two-day meeting here unless they first agreed to conditions, including an immediate halt to economic sanctions.
The standoff in this Turkish city ended with dueling diplomatic statements and deepening pessimism about prospects for solving one of the Obama administration's most vexing security challenges.
There was no discussion of further talks in the near future.
"This is not the conclusion I had hoped for," said Catherine Ashton, the European Union's foreign policy chief, after the talks ended. She acknowledged that negotiators never came close to tackling the core issues, such as Iran's uranium enrichment program, because of Iran's insistence on concessions from the West.
"These preconditions are not a way to proceed," Ashton said.
U.S. and European officials said, however, they were encouraged by the cohesion shown by the six countries on the other side of the negotiating table. Those countries -- the United States, Russia, China, Britain, France and Germany -- have often disagreed on Iran, but the group was in lockstep in their opposition to Iran's proposed conditions, according to U.S. and EU officials who participated in the talks.
The group's unanimity could enhance prospects for a broad international agreement on future sanctions or other punitive measures to force concessions from Iran in the future, the officials said.
"The Iranians are tough negotiators, and their aim was to test for splits among the six nations and to see if they could extract concessions on their preconditions," said a senior Obama administration official who participated in the meetings. "They left with a pretty clear impression of the unity of this group."
In 2002, Iranian dissidents disclosed the existence of a massive uranium enrichment plant that Iran was secretly constructing. It was the first of a series of revelations that raised questions about Iran's possible pursuit of a nuclear bomb.
Negotiations between Iran and the six world powers resumed last month in Geneva after a pause of more than a year. In those talks, Iran agreed to second round of meetings in Istanbul, raising hopes that it might be ready to consider limits on its nuclear program.