A senior Iranian envoy abruptly announced Wednesday that last-ditch talks on his country's disputed nuclear program were postponed, moving Tehran a step closer to U.N. sanctions after it defied a deadline to freeze uranium enrichment.

The talks had been tentatively set for Wednesday in Vienna as a final attempt to see if there was common ground to start negotiations between Iran and the six nations that have been trying to persuade Iran to limit its nuclear program.

But while the European Union's Javier Solana had been ready to fly to the Austrian capital at short notice, the talks had been left hanging by uncertainty over whether Iranian nuclear envoy Ali Larijani would come.

"We will not have the meeting today in Vienna," Ali Ashgar Soltanieh, the chief Iranian envoy to the International Atomic Energy Agency, told The Associated Press. "Both sides are arranging (a meeting) for a couple of days later."

There was no immediate comment from Solana's office in Brussels. But although Soltanieh said the decision to postpone any meeting had been mutual, it appeared that Iranian reluctance to attend had scuttled the chance of talks Wednesday.

In Ankara, Turkey, U.N. Secretary-General Kofi Annan, whose visit to Tehran last week failed to budge the leadership on its refusal to give up enrichment, urged Iran "to do whatever it can to reassure the international community that indeed its intentions are peaceful."

Soltanieh said "a procedural matter" had led to the postponement, but offered no details. In Tehran, Foreign Minister Manoucher Mottaki said only the time and place of any meeting continued to be "under discussion by both sides."

Iran defied an Aug. 31 deadline by the U.N. Security Council to freeze uranium enrichment.

Still, the five permanent council members and Germany — the six powers attempting to entice Iran into negotiating on its nuclear program — had decided to hold off starting work on sanctions until the outcome of any talks between Solana and Larijani.

Senior negotiators of those six countries meet in Berlin on Thursday to plan strategy.

Iran's unyielding stance appeared to be based on the calculation that sanctions will be opposed by Russia and China, both veto-wielding Security Council members that have major commercial ties with Iran. While skeptical that any new meeting between Solana and Larijani would yield success, the United States and key European allies Britain and France had agreed to wait for the result of any such talks in attempts to mollify Moscow and Beijing.

Still, with Iran remaining intransigent, even Russia appeared to be contemplating the possibility of sanctions — although comments by Foreign Minister Sergey Lavrov indicated Moscow continued to oppose harsh and quick punishment.

"We'll decide whether or not to make use of these measures in a complex way, but guided by just one goal — to prevent the proliferation of weapons of mass destruction," Lavrov was quoted as saying by the Interfax news agency. "We are also aware that economic pressure should be proportional to a real threat to peace and security."

Lavrov spoke to reporters in Johannesburg, South Africa, where he was accompanying President Vladimir Putin on a state visit.

He said the U.N. Security Council's recent resolution on Iran holds out the possibility of further measures on Iran — including those spelled out in Article 41 of the U.N. Charter. The article allows punishments that do not involve the use of armed force, such as economic penalties, banning air travel or breaking diplomatic relations.

In Beijing China's premier, Wen Jiabao, said that sanctions "may even prove counterproductive."

But U.S. officials on both sides of the Atlantic suggested the time had already come for punitive Security Council action.

State Department spokesman Sean McCormack said in Washington that the Security Council had made clear in a resolution that it was prepared to vote for sanctions if Iran failed to meet the Aug. 31 deadline to suspend enrichment.

And so, McCormack said Tuesday, the United States intended to proceed "down that pathway."

In Vienna, Gregory L. Schulte, chief U.S. delegate to the IAEA, accused Iran's leaders of making "a strategic decision to acquire nuclear weapons," adding: "The time has come for the Security Council to back international diplomacy with international sanctions."

Iran insists it has a right to enrich for generation of nuclear power. But suspicions are growing it wants to develop the technology to enrich uranium to the weapons-grade level for the fissile core of nuclear warheads.

In a further sign of Tehran's defiance, Iran's parliament took the first step Tuesday toward blocking international inspection of the country's nuclear installations in case of U.N. sanctions. The measure would need approval by other bodies before it could take effect.