The move reflects Washington’s apparent acknowledgement that it faces a tough road ahead pushing for UN sanctions against Iran.
Russia and China have put up fierce resistance to punitive measures against the Iranians.
US Undersecretary of State Nicholas Burns has stepped up the call for countries to act individually outside the UN framework.
"There are a lot of countries that trade with Iran that have billion-dollar trade relationships and they ought to begin to rethink those commercial trade relationships," he told a news briefing here.
"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. All countries should refrain from military sales and arm sales."
Mr Burns, the third highest ranking official in the State Department, singled out Russia's plans to sell Iran 29 TOR M1 mobile surface-to-air missile defence systems.
"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," he said.
Robert Joseph, undersecretary of state for arms control, said he toured the Gulf last week and held talks with regional officials on a variety of other possible measures against Iran.
Among them were efforts to intercept the transfer of sensitive materials and technologies, a crackdown on front companies and bank accounts used to aid Tehran, and greater cooperation in missile defence.
Mr Burns spoke after holding meetings earlier this week with counterparts from Russia, China, Britain, France, Germany, Italy and Canada that produced no consensus on possible UN sanctions.
The UN Security Council has given the Islamic republic until next Friday to halt its uranium-enrichment activities but has not laid out any consequences if it refused to comply.
The United States is pressing for a threat of UN sanctions such as freezes on the assets of Iranian leaders or travel restrictions.
Yet Mr Burns recognized the outcome was far from certain.
"The diplomacy here is very challenging. It is likely to extend some time into the future," he said. "I can't predict where the Security Council will be a month from today."
"It's also important for countries to know that, if for any reason the Security Council can't succeed, there will be an effort made, and there are avenues available to us to apply the kind of pressure that we need to apply."
Mr Burns said political directors of the UN Security Council's five permanent members -- the United States, Russia, China, Britain and France -- would likely meet May 2 in Paris to thrash out a strategy.
He said Iran would also be "the leading issue" when foreign ministers of the Group of Eight industrialized powers meet in Moscow in June, and G-8 leaders hold their summit in St. Petersburg the following month.
The United States has been ratcheting up its diplomatic effort againstTehran since Iran announced on April 11 it had taken a major step forward in its nuclear program by enriching small amounts of uranium.