An Iranian delegation official has said world powers are hindering talks in the Iraqi capital, Baghdad, with Iran over its nuclear programme, creating a "difficult atmosphere" as the negotiations come down to the wire.
"We believe the reason P5+1 [the permanent UN Security Council members, Britain, China, France, Russia and the United States, plus Germany ] is not able to reach a result is America," the official, who asked not to be named, told the Reuters news agency.
"[P5+1] came to Baghdad without a clear mandate so we think the atmosphere is difficult."
The meetings spilled into a second day on Thursday in apparent efforts to avoid an impasse that could derail the most promising nuclear dialogue with Iran in years.
Iran reportedly threatened to scupper efforts to defuse the crisis over Tehran's nuclear programme in the final hours of crunch talks after world powers stopped short of offering sanctions relief.
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The P5+1 want to persuade Iran to get into a process of regular meetings, hashing out details of measures aimed at easing suspicions that Tehran wants nuclear weapons.
"It seems that the basis for another round of negotiations doesn't exist yet, unless ... the two sides reach an agreement" in the final session, the official said on condition of anonymity.
The official added that before the final full plenary session of all participants began, EU foreign policy chief Catherine Ashton and Iran's chief negotiator Saeed Jalili held a bilateral meeting in which Ashton "didn't say anything new".
This week's talks were the second round in the latest series between the P5+1 and Iran over the Islamic Republic's controversial nuclear programme, with earlier negotiations held in Istanbul last month.
On the table on Thursday was an incentive package by the six-nation group that seeks to halt the most sensitive part of Iran's nuclear fuel production.
Iran insists its nuclear programme is peaceful, but Western powers suspect it is masking attempts to join the elite club of nations with nuclear weapons.
Iranian state media ran reports attacking the P5+1 package presented by Ashton on Wednesday, with the IRNA news agency calling it "outdated, not comprehensive, and unbalanced".
Ashton's spokesman gave no details on what the incentives included, but reports said they fell short of meeting Iran's key demand for an easing of the sanctions piled on the country in recent years - more are due on July 1.
Both reportedly exchanged unusually detailed proposals in Baghdad hoping to defuse the standoff.
After a 15-month diplomatic freeze and exploratory talks in Istanbul last month, envoys for Iran and the P5+1 group convened with both sides publicly upbeat about the scope for an outline deal.
The powers' overall goal is an Iranian agreement to curb uranium enrichment in a transparent, verifiable way to ensure it is for peaceful purposes only. Iran's priority is to secure an end to sanctions isolating the country and damaging its economy.
On Tuesday, International Atomic Energy Agency (IAEA) chief Yukiya Amano said an agreement with Iran over nuclear inspections was expected "quite soon" after his recent talks in Tehran.