The House of Representatives easily passed a bill on Wednesday to tighten sanctions on Iran, showing a strong message to Tehran over its disputed nuclear program days before President-elect Hassan Rouhani is sworn in.
The vote also highlighted a growing divide between Congress and the Obama administration on Iran policy ahead of international talks on the nuclear program in coming months. Iran insists the nuclear program is purely for civilian purposes.
The bill, which passed 400 to 20, would cut Iran's oil exports by another 1 million barrels per day over a year, in an attempt to reduce the flow of funds to the nuclear program. It is the first sanctions bill to put a number on exactly how much Iran's oil exports would be cut.
The legislation provides for heavy penalties for buyers who do not find alternative supplies, limits Iran's access to funds in overseas accounts and penalises countries trading with Iran in other industrial sectors.
Previous US and EU sanctions have reduced Iran's oil exports by more than half. The United States has worked with Iran's top oil consumers including China, Japan and South Korea to push them toward alternative suppliers of crude.
Oil prices have remained relatively steady, which has allowed the efforts to continue, but some analysts say further sanctions risk pushing up prices and damaging the economies of US allies.
"This is almost like an embargo on Iranian oil imports. It is like giving Iran an ultimatum," a Seoul-based refining source said, after the vote. "I think we can find alternatives but we prefer Iranian crude as the economics is better. If very little Iranian crude is available, overall oil prices would rise."
The bill still has to be passed in the Senate and signed by President Barack Obama before becoming law. The Senate Banking Committee is expected to introduce a similar measure in September, though it is uncertain whether the language to cut exports by 1 million barrels a day will survive.
Critics of the bill said it shows an aggressive signal to Iran that last month voted in Rouhani, a cleric many see as more moderate. He will be sworn in on Sunday.