US Secretary of State Hillary Rodham Clinton departed for Europe late Friday on a five day trip in which Iran, Afghanistan and arms control are expected to be subjects of discussion.
The trip will take her to Switzerland, Britain, Ireland and Russia.
During her visit to Moscow, Clinton plans to press for a strong commitment from Russia for tough new sanctions against Iran.
US officials said Iran will be at or near the top of Clinton's agenda when she meets Russian President Dmitry Medvedev and Foreign Minister Sergey Lavrov on Tuesday.
Russia and China have long balked at imposing new sanctions on Iran if it fails to come clean about its suspect nuclear program, but Medvedev hinted the Russian position might be shifting after Teheran disclosed a previously secret uranium enrichment site near the holy city of Qom.
But US officials believe it will be a hard sell to convince the Russians on fresh penalties since Iran agreed to allow UN inspectors to visit the Qom site and has agreed, in principle, to send most of its low-enriched uranium to Russia for reprocessing.
Iran agreed to allow inspections of the Qom site following talks last week between Iran's chief nuclear negotiator and diplomats from the US, Russia, China, Britain, France and Germany. The Iranians were given time to decide whether to accept a package of incentives in exchange for Iran's compliance with international demands to suspend its uranium enrichment or face new sanctions.
The Obama administration is anxious not to let up on the pressure and Clinton will be looking for Russian expressions of support for sanctions and other penalties should Iran continue to refuse by the end of the year, the officials said.
"Iran has not bought an indefinite delay and we want them to know that," said one official, who like the others spoke on condition of anonymity to preview Clinton's talks.
In remarks broadcast Friday, Medvedev said Russia does not want to see any more nations develop nuclear weapons, signaling that Moscow shares US concerns about Iran. But he said nothing about potential sanctions.
"The expansion of the 'nuclear club' is very much not in our interests," Medvedev said in a televised excerpt from an interview taped Wednesday.
In addition to Iran, Clinton will bring a wide array of other issues to Moscow, including arms control, missile defense and cooperation on convincing North Korea to abandon nuclear weapons, the officials said.
Negotiators from the two countries are racing to reach agreement on a successor to START I and Clinton wants to underscore the urgency of the talks, they said.
She also will explore possible cooperation on missile defense following President Barack Obama's decision not to proceed with Bush-administration plans to base such a system in eastern Europe. Russia had vehemently opposed those plans and has welcomed Obama's new approach.
Clinton will also join Lavrov in chairing a meeting of a commission set up by Obama and Medvedev to improve cooperation and coordination on a variety of matters, including Afghanistan.
Afghanistan is likely to dominate Clinton's Sunday visit to London, where support for military operations in the country has waned in recent months amid rising violence and allegations of major fraud in the Afghan national elections in August. Clinton will see British Prime Minister Gordon Brown and Foreign Secretary David Miliband.
In Dublin and Belfast, both of which she visited while she was first lady, Clinton will be pushing to break a deadlock between Northern Ireland's rival Catholic and Protestant leaders over transferring responsibility for Northern Ireland's justice system from British to local hands.
Clinton begins her trip in Zurich, Switzerland on Saturday where she will witness the signing of a historic pact between Turkey and Armenia to normalize relations after a century of conflict.