Clinton yesterday sought to present a united front with Russia on the Iranian nuclear crisis but Moscow stopped short of supporting tougher action if talks failed.

On her first trip to Russia as chief US diplomat, Mrs Clinton praised Moscow for its "extremely cooperative" behaviour in the standoff over Iran's programme, which western nations fear is a veiled attempt to build a nuclear bomb.

But she appeared not to win any firm public commitment from Moscow that it would back tougher sanctions against Tehran if negotiations did not make progress, something aides said ahead of her visit she had hoped to achieve.

"We didn't ask for anything today. We reviewed the situation and where it stood," Mrs Clinton said after talks with Russian Foreign Minister Sergei Lavrov.

Mrs Clinton said she agreed with Russian President Dmitry Medvedev's assessment that sanctions against Tehran may be inevitable if it defies world powers over its nuclear drive.

While describing the Iranian nuclear drive as a matter of "serious concern", Mrs Clinton appeared to move to calm Russian fears that western powers were looking to quickly impose sanctions.

"We are not at that point yet... It is not a conclusion that we have reached," she said.

But Mr Lavrov, whose country has the strongest ties with Tehran of any world power, bluntly stated that for the moment it would be wrong to talk about a fourth round of United Nations Security Council sanctions on Iran.

"Threats of new sanctions and pressure against Iran under current circumstances are counterproductive," Mr Lavrov said.

"There are situations where sanctions are inevitable, when all other avenues are exhausted. But with Iran we are very far from this," he added.

During talks with Mr Medvedev, Mrs Clinton said Washington was looking forward to "deepening and broadening" its strategic strategic relationship with Moscow.

She will not be meeting with Prime Minister Vladimir Putin, seen by most as Russia's de-facto leader, who is on a trip to China.