The meeting had been tentatively set for Wednesday in Vienna as a final attempt to see if there was common ground to start negotiations between six world powers and Iran.
This was despite Tehran's defiance of a UN security council demand that it freeze uranium enrichment.
But while the EU's Javier Solana was ready to fly to the Austrian capital at short notice, an Iranian diplomat said the talks had been postponed until at least Friday.
The talks are now likely to take place after senior negotiators of the five permanent members of the security council plus Germany meet in Berlin on Thursday to plan their policy towards Iran.
Sergei Lavrov, Russia's foreign minister, said on Wednesday that any economic sanctions adopted against Iran over its nuclear programme must rule out the use of force.
Lavrov, speaking to reporters on a visit to South Africa, said any sanctions would be governed by the United Nations charter which "states unequivocally that economic measures exclude the use of force".
In Berlin, Angela Merkel, the German Chancellor, said Iran could not be allowed to damage the UN with its refusal to heed calls to suspend enrichment.
Merkel said that Iran's response to an offer of incentives and refusal to freeze nuclear enrichment work was unacceptable.
The chancellor said: "Iran's response is not satisfactory. We won't close the door to negotiations but we the international community won't stand by and watch as Iran harms the rules of the UN nuclear authorities."
However, she reiterated that military action was not an option.
Iran fighter jet
In a separate development, Iran has announced that it has developed a new aircraft named Saegheh (Thunder), which it described as close to the American F-18 fighter jet.
General Attollah Salehi, the commander of the Iranian army, was quoted by the state news agency IRNA as saying the fighter jet is similar to the F-18, but more capable. It was manufactured domestically.
Iranian state television reported that the jet "is able to fire rockets and also to drop bombs and is equipped with an advanced radar system".
"The fighter jet Saegheh, after successful military operations and accurately firing air-to-surface rockets in the Zolfaghar Blow manoeuvres came into the service of the Iranian air force today," the report said.