International negotiations over Iran's alleged nuclear weapons program are stalled, according to experts on the issue, and there are deep divisions about what to do next.
The latest negotiating session, bringing together representatives from the United States, Russia, China, Britain, France, Germany and Iran, was held last month in Baghdad. Very little progress was achieved with the next meeting scheduled in Moscow for mid-June.
The United States and the European Union believe Iran's uranium enrichment program is designed ultimately to build nuclear weapons. Tehran rejects that view, saying it wants to use its enriched uranium for peaceful purposes, such as electricity.
The conventional wisdom is that Russia's economic interests in Iran have led Moscow to be a strong supporter of that country.
But at the same time, experts say since the beginning of the Obama administration, Russia has gradually toughened its stance on Iran, voting at the United Nations to establish stricter sanctions against Tehran.
"The U.S.-Russian position on Iran and the challenge of Iran's program, officials within the administration tell me, is as close as it has ever been," says Robert Legvold of Columbia University.
However Legvold says there are still disagreements between Washington and Moscow, especially about the idea of a military strike against Iran.
"The Russians are very antsy [nervous] about such an idea," he says, "whether it's Israel that executes it or whether it is some kind of a U.S. option, or the U.S. with Israel together."
Legvold says Moscow also continues "to push much harder on the diplomatic option rather than further tightening of sanctions."
Stephen Cohen, professor emeritus at Princeton University and New York University, says Moscow did more than vote for tougher economic sanctions.
"Russia cancelled a deal it had with the Iranian government to supply it with anti-aircraft missile," says Cohen, "the kind of anti-aircraft missiles that Iran would need to defend itself if it was attacked by Israel or the United States, which remains, by the way, on at least the theoretical agenda."
Those were "enormous concessions by Moscow," says Cohen.
But experts say one area where Moscow will not compromise, is missile defense - a U.S.-led concept closely linked to the Iran nuclear issue.
In an effort to counter the possible nuclear missile threat from Tehran, the Obama administration's plan calls for deploying a system of anti-missile interceptors based at sea on destroyers and cruisers and coupled with advanced land-based versions, some of which would be based in former Warsaw Pact countries.
Russia has consistently opposed U.S. plans for a ballistic-missile defense system in Europe. Moscow does not believe the goal is to defend against missile attacks from such countries as Iran. Russian officials see the U.S. project as aimed against Moscow's nuclear missiles - a charge denied by the United States.
Experts, such as Robert Legvold, say Moscow's criticism is with the last phase of the deployment scheduled for 2020.
"That is an intercontinental [anti-]ballistic missile system designed to defend the entire continent," says Legvold. "And those, theoretically, depending on where they are deployed, could be something of a threat to the Russian nuclear deterrent."
At the recent NATO summit in Chicago, leaders reaffirmed their commitment to the missile defense shield. Russian President Vladimir Putin was invited but did not attend. Some experts say he stayed away to emphasize his opposition to the missile defense shield.