Russia has ruled out sanctions against Iran unless there is proof that its nuclear programme is not peaceful.
Russia is helping Iran build a civilian nuclear plant
Mikhail Kamynin of the foreign ministry said Russia would have to see "concrete facts" proving military intent.
The US is trying to rally support from UN Security Council members, including Russia, to back tougher action on Iran.
The UN says there is so far no proof that Iran is seeking nuclear weapons - as suspected in the West - but nor has Iran proved that it is not.
"Sanctions can be discussed only when there are concrete facts showing that Tehran's nuclear activity is not exclusively peaceful," Mr Kamynin said in Moscow.
"At the present time, the concerns of the international community over the Iranian nuclear program cannot be eased through sanctions and use of force."
The UN Security Council is awaiting a report from Mohamed ElBaradei, the head of the International Atomic Energy Agency (IAEA), assessing Iran's nuclear activities, before deciding its next move. The report is due in a week's time.
In resolutions on Iran the IAEA has said:
There is an "absence of confidence that Iran's nuclear programme is exclusively for peaceful purposes"
Iran had failed to meet obligations on reporting of nuclear activities, and had a "policy of concealment"
The agency was "still not in a position to conclude that there are no undeclared nuclear materials or activities in Iran"
Tehran has defied UN calls to stop nuclear activity, saying last week it had successfully enriched uranium. However it denies any nuclear weapons plans, saying it wants nuclear power only for energy purposes.
Iran's ambassador to the IAEA said on Friday Tehran would "continue its full co-operation" with the body.
But the IAEA says Iran has not co-operated fully, and one of its senior inspectors has called off a visit to the country that was supposed to have taken place on Friday.
There was no point in Olli Heinonen making the trip "if he's just going to get stonewalled", an EU diplomat told Reuters.
Mr Kamynin's comments in Moscow came after meetings there between the main Security Council powers and other major players, to discuss the next steps in the Iran crisis.
While the countries stress the need to maintain a united front, however, differences have opened up.
The US called on Russia to end assistance it is giving Iran with its civil nuclear programme, and to suspend a major arms sale to Tehran.
Russia refused on both counts, and repeated its opposition to any military strike on Iran, which the US has not ruled out.