By Christian Lowe

MOSCOW (Reuters) - Hitting Iran now with sanctions over its nuclear work could drive it "away from the civilised world", a Kremlin official said on Tuesday, in a hint of strong Russian opposition to punitive steps backed by Washington.

China said earlier it still wanted major world powers to negotiate with Iran even after it defied a U.N. Security Council deadline of Aug. 31 to stop enriching uranium.

The Chinese and Russian stances underlined the obstacles to a U.S.-led push to consider sanctions against Iran this month in the Council, where Beijing and Moscow wield vetoes.

Washington's EU allies, also hesitant about sanctions, were looking to talks this week to explore hints by Iran that it could negotiate over the extent of its nuclear fuel programme, which the West fears is a disguised bid to build atom bombs.

European Union foreign policy chief Javier Solana was tentatively expected to meet Iran's chief nuclear negotiator Ali Larijani in Vienna on Wednesday.

But diplomats said the day and venue for the talks could still change and nothing had been finalised by late on Tuesday.

Tehran, the world's fourth largest oil exporter, says its enrichment of uranium is a legal and peaceful programme to meet civilian energy needs. The United States says it is a front for perfecting technology designed to produce nuclear weapons.

"That's our judgment. Now, there's not 100 percent certainty there. We've been wrong in the past with our judgments," Gregory Schulte, U.S. ambassador to the Vienna-based U.N. watchdog, the International Atomic Energy Agency (IAEA), said on Tuesday.

But, he told reporters, Iran's record of concealing its nuclear work from IAEA inspectors permitted no other conclusion.

"Sanctions are not the end of diplomacy. (But) ... to be successful, diplomacy must now be backed up by sanctions, applied in a graduated fashion and targeting Iran's weapons programme and those who guide it," said Schulte.

Igor Shuvalov, a senior aide to Russian President Vladimir Putin, did not say at a news briefing how Russia might vote in the Council but he issued an unusually detailed defence of Moscow's opposition to sanctions.

RUSSIAN WARNS AGAINST BLOWBACK

"We are for using a stick (against Iran) but we do not want to later get hit on the head by that same stick, or that it should hit any of our partners on the head," he said.

"At the moment we have understood that introducing sanctions now or resorting to a military operation could lead to the ... consolidation of the population around the current leadership.

"In Iran the majority of the population are young people and any careless actions could drive that country away from the civilised world for many decades," Shuvalov said.

"If at the moment the talk is of developing a peaceful (nuclear) programme, then, in the event of a military operation, you could hear very different statements. When 60 million people support that sort of thing, it is quite dangerous."

Shuvalov did not rule out Russia at some point backing sanctions. But he said the international community must "show particular caution and responsibility".

Russia has a lucrative contract with Tehran to build a nuclear power station at Bushehr, on the Gulf. Moscow sells arms to Iran and Russian oil companies have interests in the country.

Chinese Premier Wen Jiabao said resolving the nuclear issue required committed diplomatic negotiations.

"But imposing sanctions will not necessarily get us there, and may even prove counter-productive. The parties involved should be cautious about moving towards sanctions," Wen told Reuters and a small group of foreign media.

China's trade with Iran reached nearly $8 billion in the first seven months of the year.

Germany has publicly signalled it is losing patience with Iran and the United States has said it is consulting European allies about possible sanctions against the Islamic state.

But diplomats say there is scant enthusiasm for sanctions in the 25-nation EU, given Iran's position as a major oil supplier to the bloc and as a market for EU exports, as well as a sense that diplomatic possibilities may not yet be exhausted.

EU officials said Solana would try to clarify Iran's stance, made in an Aug. 22 reply to a six-power offer of trade incentives not to enrich uranium, by mid-September.

Schulte warned against allowing Iran to play for time.

(Additional reporting by Lindsay Beck, David Schlesinger and Brian Rhoads in Beijing, Mark Heinrich in Vienna and Mark John in Brussels)