A mooted deal between the IAEA and Iran got a cool reception Tuesday on the eve of talks with world powers aimed at defusing the dangerously escalating crisis over Tehran's nuclear programme.
Yukiya Amano, International Atomic Energy Agency head, said on returning from Tehran that he and Iran's chief nuclear negotiator made a "decision" to reach an agreement on the UN watchdog probing suspected weapons activities.
But contrary to the hopes of some diplomats before he left on Sunday, Amano failed to actually sign a deal, saying at Vienna airport that this would happen "quite soon" because of remaining, unspecified "differences."
The United States expressed caution, saying the proposed agreement marked a "step forward" but that Tehran would be judged on its actions.
"It's important to note that the announcement today is a step forward," White House spokesman Jay Carney said, calling the planned deal between the IAEA and Iran "certainly significant."
However, "we will make judgments about Iran's behavior based on actions."
A key demand of world powers is that Iran address accusations in a major IAEA report in November that, until 2003, and possibly since, Tehran did work "relevant to the development of a nuclear explosive device."
One Western diplomat told AFP there had been "no breakthrough" in Amano's visit. Another said the trip appeared disappointing but that they were waiting for a "clearer picture" at meetings in Vienna later on Tuesday.
"This is only a promise, and Iran has made many, many promises in the past," said a third, adding that Tehran was possibly trying to appear cooperative ahead of Wednesday's meeting in Baghdad.
The US mission in Vienna said that while it appreciated Amano's efforts, it was "concerned by the urgent obligation for Iran to take concrete steps to cooperate fully" with the agency, a point underlined by the State Department.
Washington will look for Tehran to "provide the access to all of the locations, the documents, and the personnel that the IAEA requires in order to determine whether Iran's program is exclusively for peaceful purposes," State Department spokeswoman Victoria Nuland told reporters.
Israel is "highly sceptical" about the deal, a senior official told AFP on Tuesday, with Finance Minister Yuval Steinitz saying Iran has played "hide-and-seek for years" with the international community and the IAEA.
Mark Hibbs, proliferation expert at the Carnegie Foundation for International Peace, told AFP "the negotiation isn't over and done with until it's signed on the dotted line."
"Amano has to be extremely careful he doesn't forfeit any rights to Iran for the sake of getting an agreement. That would serve as a bad precedent."
Amano also said access to the Parchin military site near Tehran, where the IAEA believes some weapons work took place, and which the agency has made a point of seeking to inspect, would "be addressed."
On Wednesday, the P5+1 -- Britain, China, France, Russia and the US plus Germany -- hope Iran will agree to a series of steps that can allay once and for all suspicions that it wants the bomb, most notably uranium enrichment.
Tehran says its nuclear programme is for purely peaceful purposes.
In particular, they would like a suspension of enrichment to 20 percent, a capability that in theory makes it relatively easy to enrich to weapons grade -- 90 percent -- if it decided to develop a nuclear arsenal.
Iran on Tuesday announced it was loading domestically produced, 20-percent enriched uranium fuel into its Tehran reactor, underlining its atomic progress.
Shipping its uranium stockpiles abroad, and implementing the additional protocol of the nuclear Non-Proliferation Treaty, which allows for more intrusive IAEA inspections, are considered other ways in which Iran could build confidence.
But Iran will likely be disappointed if it expects to see sanctions relief in return for any of these moves, with the most it can hope for being a pledge -- with strings attached -- not to impose any more, diplomats said.
In any case, it is far from certain that any firm promises will be made from either side in Baghdad, with one envoy playing down expectations by saying that even if the talks go well, the results might not be "tangible."
Instead, the outcome could be an agreement to hold more regular talks at a working level to thrash out the technical details of confidence-building measures, a process needing two vital and elusive elements: patience and trust.
Israel, meanwhile, widely believed to have nuclear weapons itself, is concerned the P5+1 might eventually tolerate Iran enriching uranium, something which it has made clear is a "red line."
"Iran threatens Israel, peace and the entire world. Against this malicious intention, the world's leading countries must show determination, not weakness," Premier Benjamin Netanyahu said late on Monday.
In Baghdad, meanwhile, a sandstorm closed the airport, casting doubt on whether the talks would begin on schedule and be completed in one day.