Iran says it only wants nuclear power for peaceful purposes
The US Senate has backed legislation allowing President Barack Obama to extend sanctions against Iran.
The new sanctions would target those who export fuel to Iran.
In his first State of the Union address on Wednesday, Mr Obama warned Iran's leaders of "growing consequences" over its nuclear programme.
The US and its allies fear Iran is attempting to develop nuclear weapons. Iran insists its nuclear programme is entirely peaceful.
The Senate bill targets non-Iranian companies that export fuel to Iran or help expand Tehran's oil refining capacities by denying them US loans and other financial assistance.
The Senate backing follows legislation approved in the House of Representatives and the two must be reconciled before they can become law.
On Wednesday, Mr Obama said that "Iran's leaders continue to ignore their obligations", in an apparent reference to Tehran's nuclear activities.
He warned that Iranian leaders would "face growing consequences. That is a promise".
US Secretary of State Hillary Clinton, who is in London, said: "Our efforts to apply pressure on Iran are not meant to punish the Iranian people. They are meant to change the approach the Iranian government has taken toward its nuclear programme."
The BBC's Jon Bithrey says the vote is a sign that US lawmakers want to get tougher on Tehran, with sanctions that would target firms anywhere in the world that provide Iran with refined fuels such as petroleum.
Earlier this month, Iran told the UN nuclear watchdog, the International Atomic Energy Agency (IAEA), it could not accept the terms of a deal to ease concerns about its programme.
For months, the Iranian government had criticised the offer to ship low-enriched uranium abroad in return for fuel, but never responded formally.
There have been three rounds of UN sanctions against Iran and the US and its allies on the Security Council have been pushing for a fourth.
In 2006, the council called on states to block Iran's import and export of "sensitive nuclear material and equipment" and to freeze the financial assets of those involved in Iran's nuclear activities.
In 2008, the council banned all of Iran's arms exports.
Further restrictions - imposed in March 2008 - encouraged scrutiny of the dealings of Iranian banks.