By Kim Ghattas
BBC News, Moscow
Hillary Clinton came to Moscow for a day of intensive talks with Iran at the top of her agenda, hoping to build on a recent warming of relations with Russia under the Obama administration.
Mrs Clinton praised Russia help - but there was no movement on sanctions
Officials travelling with her said she wanted to assess Russia's position on adopting a tougher stance on Iran and its controversial nuclear programme.
"The secretary will want to speak to Foreign Minister Lavrov and President Medvedev about what specific forms of pressure Russia would be prepared to join us and other allies if Iran fails to live up to its obligations," a US official told reporters ahead of the arrival.
Instead of detailing the specifics of action or support for sanctions, after almost three hours of talks with Mrs Clinton Sergei Lavrov told a press conference: "Our position is that at this stage all efforts should be made to support the negotiating process."
"Sanctions and the threat of pressure in the current situation are counter-productive in our view," he added.
After the US, Britain and France announced last month that Iran had failed to disclose a uranium enrichment facility in Qom, President Dmitry Medvedev signalled a shift in position, saying sanctions were "sometimes" inevitable.
It was read in Washington as a direct reaction to revelations about the covert facility.
Iran has agreed to allow IAEA inspectors into the facility at Qom
"Qom was a giant surprise for the Russians," said one senior administration official.
Asked if they were angry when they were told by President Barack Obama about the facility during a meeting in New York last month, on the sidelines of the UN General Assembly, he said that would be an appropriate word to describe the reaction.
It is unclear why the Russians did not have any intelligence of their own about Qom.
"The people who were in the room [with Mr Obama] did not know about it, but I don't know about other Russians."
Pundits and experts wondered out loud whether Russia had finally come to see Iran the way Washington did and speculation grew about whether Moscow would support sanctions.
These developments came shortly after the Obama administration announced it was scrapping a missile defence shield plan based in Poland and the Czech Republic, which had considerably angered Moscow.
While the US insisted it was not a quid pro quo with Russia, the decision did seem to add a lot of warmth to a relationship which had turned frosty under the Bush administration.
During the UN General Assembly in New York last month, Mr Medvedev even expressed his appreciation. Mr Obama's plans to push the restart button on ties with Russia seemed to be working.
But suddenly in Moscow it looked like the White House was not getting anything in return, raising the question - had Russia shifted back to its original position of opposing sanctions?
The shift is partly explained by Iran's own actions. During talks in Geneva after the Qom revelation, it agreed in principle to allow inspectors from the International Atomic Energy Agency (IAEA) into the facility.
US officials said Russia appeared unaware of the second facility at Qom
It also agreed to send most of its low-enriched uranium out of the country to be processed into fuel abroad. This immediately eased the pressure on Iran and allows Russia to say it is not time for sanctions yet.
After Mr Lavrov's comments, US administration officials insisted they had not come seeking any specific actions or promises, despite earlier briefings.
The senior official said they wanted a public statement from the Russians about the threat of sanctions and got that in New York. "We're not asking for more at the moment," the official said.
Several members of the US delegation, all speaking on condition of anonymity, said they did sense a real change in Russia's position that was very different from the scepticism of recent years over the threat that Iran posed.
Proof of that was Russia's backing for the low-enriched uranium (LEU) plan, said the US official, pointing that if Russia was not concerned it would not have supported taking Iran's LEU out of the country.
He added there had been a "dramatic" change in Russia's assessment of the threat posed by Iran.
But another official agreed that differences remained about how to talk to Tehran; while Americans use tough words, Russians fear it will only cause the Iranians to dig in their heels.
This may considerably weaken the image of a united front which Washington is seeking and take the heat even further off the Iranians.
The Washington Post's Fred Hiatt recently wrote that the Russians had "consistently dangled the possibility of co-operation with the United States while simultaneously undermining alliance unity and maintaining their connections to the Iranian regime".
He listed quotes from successive American officials over the years who made public statements about their belief that Russia was finally starting to see eye with America on Iran.
He warned that the smartest policy for the Russians was similar to what they were currently doing - "to hold out hope to the Obama administration that they can be brought along - thereby continuing to win US concessions on other matters for as long as possible - while seeking a privileged position in Tehran for the day when Iran goes nuclear".
Russia and Iran also share some interests in the region, so Moscow is not necessarily eager to alienate Tehran too much.
It can also give the impression it is willing to play along, because it knows China is not ready for sanctions yet and could do all the stalling.