The US senate has passed a bill approving the tightening of sanctions on Iran.
The sanctions are designed to put pressure on Iran to halt its nuclear programme.
The bill will make it mandatory for US firms to disclose any business related to Iran and will target the Iranian Revolutionary Guard and its activities.
"Today the US Senate put Iranian leaders on notice that they must halt all uranium enrichment activities or face another round of economic sanctions," Republican senator Mark Kirk, a co-author of the bill, said in a statement.
The bill was passed just a few days before critical talks are due to take place on Iran’s nuclear programme, which has prompted some analysts to criticise the move by the US Senate.
"The biggest requirement now for getting an agreement is not to pile on still more sanctions, but instead to persuade the Iranians that if they make concessions the sanctions will be eased," said Paul Pillar, a security studies professor at Georgetown University.