Iran says its nuclear programme is for peaceful purposes
The US House of Representatives has overwhelmingly approved new sanctions against Iran aimed at halting its disputed nuclear programme.
The measure empowers President Barack Obama to ban foreign firms that supply Iran with refined petroleum from doing business in the US.
The bill, which passed 412-12, can only become law if approved by the Senate.
The measure expands an existing US law that punishes any firm that invests $20m a year in Iran's energy sector.
Iran has one of the world's largest oil reserves but it lacks refining capacity and imports 40% of domestic fuel needs.
It gets most of those imports from European firms such as Vitol, Trafigura, Total and British Petroleum.
Under the proposed new sanctions, firms could be banned from doing business with the US or blocked from receiving financial assistance from American institutions.
The BBC's Richard Lister in Washington says the bill is a warning to Iran that Congress is serious about imposing significant sanctions unless the Iranian leadership demonstrates that it is not seeking nuclear weapons.
Critics of the legislation say it could backfire and lead to Iranian citizens blaming the US for any supply shortages.
"This will unify the Iranian people against us," said Republican Representative Ron Paul, who opposed the measure.
But House Speaker Nancy Pelosi said the measures sent a clear signal to Iran that Washington would use all the tools at its disposal to stop it from achieving a nuclear capability.
"We must use all the tools at our disposal, from diplomacy to sanctions, to stop Iran's march toward nuclear capability," she said.
Iran is already subject to UN sanctions over its nuclear programme, which the West suspects is for military purposes.
Tehran has insisted its nuclear programme is for purely peaceful purposes and has warned that further sanctions will be ineffective.