— A faltering diplomatic effort to persuade Iran to curtail its nuclear program was salvaged Thursday by an agreement to hold further talks next month in Moscow, concluding two days of negotiations that exposed the difficulty of bridging the chasm between Tehran’s ambitions and the West’s demands.

Addressing reporters at the close of the marathon talks, European Union foreign policy chief Catherine Ashton acknowledged that “significant differences” remain over how to address international concerns about Iran’s nuclear activities. However, she said there was “some common ground” and took heart that Iran had agreed to further talks.

“What we have now is some common ground and a meeting in place where we can take this forward,” she said.

The talks in Baghdad — between Iran and world powers United States, Russia, China, Britain, France and Germany — had been accompanied by high hopes that the current climate was conducive to progress on a deal that would help ease a decade of tensions over Iran’s nuclear activities and lift the threat of war hanging over the Middle East.

But the negotiations snagged early on as Iran rejected a package of proposals put forward by the world powers as inadequate because it offered no immediate relief from crippling economic sanctions, nor any acknowledgment of the right Tehran claims to enrich uranium.

Chief Iranian negotiator Saeed Jalili called the talks “thorough but unfinished.” He said Iran was not prepared to make any concessions unless the six nations accept “the undeniable right of the Iranian nation . . . to enrich uranium.” U.S. officials said that is not a concession they are prepared to grant.

Jalili also made it clear that Iran would not countenance a deal that did not alleviate the sanctions that have been taking an increasingly devastating toll on the country’s economy.

“We believe the pathway to talks can be successful only if destructive pathways working in parallel with the pathways are stopped,” Jalili said. “This strategy of pressure is over. It is outmoded.”

Iran did concede, however, that it is open to negotiations about the level to which it will continue to enrich uranium. Iran has the capacity to enrich uranium up to 20 percent, which puts it within technical reach of the 90 percent level required for the fissile material used in nuclear weapons.

If world powers acknowledged Iran’s right, Jalili said, “this enrichment . . . could be an issue of cooperation and talks.”

Ashton said the six world powers had put forward proposals concerning “what could be done around the 20 percent” enrichment level, suggesting that the issue could be addressed further at the Moscow talks, scheduled for June 18-19.

‘A lot of work still to do’

In Washington, administration officials acknowledged that the talks had not produced anything close to the breakthrough some had hoped for. Secretary of State Hillary Rodham Clinton said that the negotiations had been “serious” and “substantive” but that significant gaps remained.

“We think that the choice is now Iran’s to work to close the gaps,” Clinton told reporters at the State Department. “We anticipate there will be ongoing work between now and the next meeting in Moscow, but it’s very clear that there’s a lot of work still to do.”

The bright spot of the two days of talks, she said, was the unity of the six powers in dealing with Iran. In contrast with previous such efforts, the six nations were “speaking literally off the same page and with the same voice” in Baghdad, she said.

Much of Thursday was spent haggling over the venue for the next round of talks. The six-nation bloc insisted on Geneva, but Iran refused to join in negotiations in any country that had supported sanctions against the Islamic republic.

The mood seemed to lift somewhat during the day, and a U.S. official said that after one of the group sessions, Jalili paused to chat with the chief U.S. negotiator, Wendy Sherman, marking a rare direct encounter between representatives of two nations estranged for more than three decades.

The effort was aided in part by a dust storm that enveloped Baghdad, forced the closure of the airport and prevented delegates from departing, stretching what had been intended as a two- hour morning session well into the evening.

The delegates were also driven, U.S. officials said, by a sense of urgency to keep diplomacy alive at a time when Israeli threats to bomb Iranian nuclear facilities have raised fears that war could be imminent.

“There is nobody . . . that does not understand the enormous pressures and the enormous stakes,” said a senior U.S. administration official, speaking on the condition of anonymity. “We are urgent about it because every day we don’t figure this out is a day they are going with their nuclear program.”

Intractability vs. flexibility

The chasm between the six powers and the Iranians on such core issues as sanctions and uranium enrichment deepened pessimism about the likelihood of a deal.

“The West can’t give enough on sanctions, and Iran won’t concede enough on the nuclear side — at least not yet,” said Aaron David Miller, a former senior adviser to the State Department on Middle East issues. In the meantime, he said, the talks are being kept alive as a “management exercise driven by Iran’s vulnerability and need for sanctions relief and the West’s fear of war.”

But others drew hope from both sides’ willingness to continue talking.

“An initial confidence-building deal is still within reach if both sides show some flexibility,” said Daryl G. Kimball, executive director of the Arms Control Association, a Washington nonprofit organization.

“While an agreement on initial confidence-building steps was not reached in Baghdad, it is clear that both sides are exchanging serious proposals that could produce results in the next round.”

Warrick reported from Washington.