Talks between Iran and the EU over Tehran's nuclear programme have been postponed for several days, Iranian envoys say.
Iran insists its nuclear programme is purely civilian
They are now likely to take place after top UN powers meet on Thursday to discuss the deadlock over Iran.
The US is pushing for sanctions against Tehran, which it fears wants to develop nuclear weapons. Iran denies this.
Russia has now said it will consider supporting economic sanctions against Tehran for defying UN resolutions.
Iran ignored a 31 August deadline, set by the UN Security Council, to stop uranium enrichment.
Russian Foreign Minister Sergei Lavrov said on Wednesday that Russia was considering supporting UN economic sanctions.
"We will consider this from all points of view, in totality, based on our goal of not allowing the spread of WMD [weapons of mass destruction] and technology that is linked with this," he was quoted as saying by Russia's state-run RIA Novosti news agency.
This appeared to be a hardening of Russia's position. It has previously signalled that it might oppose sanctions.
The talks in Vienna - originally set tentatively for Wednesday - had been described as a last chance for Iran to avoid sanctions over its enrichment of uranium in contravention of UN orders.
"We will not have the meeting today in Vienna, but it will be held in a couple of days" in Vienna, the Iranian ambassador to the International Nuclear Energy Agency, Ali Asghar Soltanieh, said.
There was speculation it could take place on Friday.
He would say only that "a procedural matter" had caused the delay.
"It is more appropriate for both sides to meet later," he said.