Iran threatened on Thursday to scupper efforts to defuse the crisis over Tehran's nuclear programme in the final hours of crunch talks in Baghdad after world powers stopped short of offering sanctions relief.
The P5+1 -- Britain, China, France, Russia and the United States plus Germany -- want to persuade Iran to get into a process of regular meetings hashing out details of measures aimed at easing suspicions Tehran wants nuclear weapons.
But after EU foreign policy chief Catherine Ashton on behalf of the P5+1 laid out a set of proposals on Wednesday that appeared to alarm Tehran, an Iranian official said there was currently insufficient agreement for another meeting.
"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, Ashton and Iran's chief negotiator Saeed Jalili held a bilateral meeting in which the Briton "didn't say anything new."
The talks were expected to wrap up around 10:00 am (0700 GMT), officials said, but appeared to be running over. They were originally meant to be completed on Wednesday but were extended after talks went late into the night.
"There have been some areas of common ground and there has been a fair amount of disagreement," said a senior US official late Wednesday, portraying this as a sign that the negotiations at least were as serious as hoped.
"We have engaged in a lot of back and forth. Some of that has been difficult but any negotiation that is worth its salt is difficult because you are getting down the issues that matter. We are the beginning of this process. We are not in the middle of it and we are certainly not at the end of it."
The new proposals was thought to include the demand that Iran suspend uranium enrichment to 20 percent, the part of its nuclear work that most raises suspicions that the Islamic republic is bent on having an atomic arsenal.
In return world powers were prepared to offer various sweeteners but not Iran's key demand of relaxing some of the UN Security Council and unilateral sanctions piled on the Islamic republic in recent years.
Instead they reportedly proposed a pledge not to impose any new sanctions, as well as easing Iranian access to aircraft parts and a possible suspension of an EU insurance ban on ships carrying Iranian oil.
It also reportedly included a revival of previous attempts to get Iran to ship abroad its stockpiles of enriched uranium in return for fuel for a reactor producing medical isotopes.
But Iran announced on Tuesday that it was loading domestically produced, 20-percent enriched uranium fuel into the reactor, and the Iranian official in Baghdad was dismissive of reviving the idea of a swap.
"A possible swap of uranium enriched by Iran for fuel isn't very interesting for us because we are already producing our own fuel," the Iranian official said.
Iran made a five-step counter-proposal that an official said was "based on the principles of step-by-step and reciprocity", which Iran's ISNA news agency called "comprehensive... transparent and practical".
The Baghdad talks were always going to be tough, as to make progress the two sides would have to tackle some of the thorny issues that have divided them -- and the P5+1 themselves -- for years.
One key way for Iran to win the confidence of the P5+1 would be to implement the additional protocol of the nuclear Non-Proliferation Treaty, which allows for more intrusive inspections by the International Atomic Energy Agency.
The IAEA also wants Iran to address allegations made in its November report that until 2003, and possibly since, Tehran had a "structured programme" of "activities relevant to the development of a nuclear explosive device".
IAEA chief Yukiya Amano said on Tuesday after talks in Tehran that a deal on ways to go over these accusations with the Iranians would be signed "quite soon". Western reaction though was cool.