"Nearly every country is considering some sort of sanctions and that is new," US Under Secretary of State Nicholas Burns said after two days of talks in Moscow with other UN powers and Group of Eight members.
But the US and Russia emerged from the meetings at odds over how to proceed. The US has been prodding Moscow to halt civilian nuclear cooperation with Tehran while Russia has ruled out the use of military force.
Russia is Iran's biggest nuclear partner and is building the country's first atomic power station at Bushehr.
The head of Russia's armed forces said his country would not take sides if the current Iran crisis led to a military conflict.
"Of course Russia will not, at least I as head of the general staff, suggest the use of force on one side or the other, " chief of general staff General Yury Baluyevsky said.
Diplomats went into the Moscow talks repeating calls to build a united front in order to keep Tehran from exploiting their divisions to forge ahead with uranium enrichment.
Iran insists its program is peaceful, but Western powers, led by the
United States, suspect it of developing a secret atomic weapons program.
Call for unity
British Prime Minister Tony Blair had earlier called for a show of unity from the world powers huddled in Moscow.
French Foreign Minister Philippe Douste-Blazy also warned that the veto-holding UN Security Council permanent members, Britain, China, France, Russia and the US, must be together if they were to dissuade Iran.
"If, on the contrary, the Chinese and the Russians, if the international community is not united it makes it easy for the Iranians to continue" to defy international demands to halt the program, he said.
Paris and London were also quick to stress that use of force was not on the table.
Russia and China, both of whom have strong trade ties to Iran, have shown extreme reluctance to threaten the use of force or even sanctions against the regime.
But Mr Burns refused to rule out unilateral action by Washington but said it would be "best" to work with other countries in doing so.
He also urged Moscow not to go ahead with the delivery to Iran of a consignment of Tor-M1 mobile air defence systems, only hours after General Baluyevsky confirmed that deal would go through.
Tehran, which has resumed its nuclear activities in defiance of a UN demand for a freeze, announced last week it had successfully enriched a small amount of uranium for use as nuclear fuel.
Surprise talks
Meanwhile, Britain, France and Germany, the European Union negotiating team called the EU-3, held surprise talks in Moscow with an Iranian delegation.
An Iranian delegation arrived in Moscow, led by deputy foreign minister Abbas Araghchi and aides to Iran's top nuclear negotiator Ali Larijani.
A senior French official told AFP after the meeting that Iran planned to step up uranium enrichment work soon and had asked European countries to participate in this effort.
Meanwhile the UN Security Council is awaiting a report due by April 28 from Mohamed ElBaradei, the head of the UN watchdogy, the International Atomic Energy Agency, on whether Iran has complied with its demands to freeze uranium enrichment.
Iran insists its program is peaceful, but enrichment can be extended from making reactor fuel to the production of warheads.