Washington has asked Moscow to reconsider selling Iran anti-aircraft missiles as the crisis over its nuclear programme continues.
Iran's military plans are a matter of concern to Washington
Russia plans to sell Tehran 29 TOR M1 mobile surface-to-air missile defence systems in a deal said to be worth about US $700 million (£392m).
"This is not time for business as usual with the Iranian government," a top US state department official said.
The US also urged other states like China to review defence sales to Iran.
"There are a lot of countries that allow the export of dual-use technologies, and the position of the United States is that should be prohibited," said Undersecretary of State Nicholas Burns.
"All countries should refrain from military sales and arm sales."
Speaking about the Russian missiles, he said:
"We hope and we trust that that deal will not go forward because this is not time for business as usual with the Iranian government."
Russia and China are both strongly resisting attempts to impose United Nations sanctions on Iran, which the US and other Western states believes is pursuing nuclear weapons.
The US arms appeal is a sign of increasing concern in Washington at the speed with which Iran is pursuing its programme, the BBC's Jonathan Beale reports from Washington.
Russia says it has to see concrete proof that Iran's nuclear programme - which it is supplying with technology - is not peaceful.
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"
The UN's position is that so far no proof has emerged that Iran is seeking nuclear weapons but nor has Iran proved that it is not.
The UN Security Council is awaiting a report from Mohamed ElBaradei, head of the International Atomic Energy Agency (IAEA), next week.
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.