MOSCOW -- Iran on Monday offered up a blistering critique of a proposal by six world powers to rein in Tehran’s nuclear program, marking another setback in efforts to find a diplomatic solution to the dispute.

In its first detailed analysis of the proposal, Iranian chief negotiator Saeed Jalili enumerated a lengthy list of objections in a five-hour negotiating session at a Moscow hotel and expounded at length about Iran’s grievances with the West dating back to 1968.

The meeting, the third this year between Iran and the six powers, “was intense, it was tough,” said Michael Mann, a spokesman for the European Union’s foreign policy chief, Catherine Ashton. He said that the Iranians had finally engaged on the offered proposal, but “it was not discussed in quite the way we had hoped at this stage.”

He said that both sides would “reflect” overnight and then would gather again Tuesday to consider their next step and weigh whether it still made sense to schedule another round of talks.

Diplomats for the six powers -- Britain, France, Russia, China, Germany and the United States -- cautioned that the objections may not be as much of a blow to the talks as it appears, noting that Iran sometimes turns conciliatory after public belligerence.

“They have reason to want these talks to continue too,” said a senior Western diplomat who requested anonymity, which is common during such negotiations.

Nevertheless, the Iranian critique -- rolled out in a PowerPoint presentation -- extended a losing streak for efforts to resolve the dispute. Last month in Baghdad, the Iranians dashed hope for quick progress by complaining bitterly in a negotiating session about their treatment on the nuclear issue and catalogued grievances unrelated to the topic.

Even a temporary halt in the talks could upset nervous oil markets and stir renewed talk about a possible Israeli air attack to end the threat Israel sees from the Iranian nuclear program.

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-- Paul Richter

Photo: Iranian chief negotiator Saeed Jalili takes part in the high-stakes talks on Iran's nuclear program, in Moscow on Monday. Credit: Kirill Kudryavtsev / Pool photo