US energy services company Halliburton is to end its operations in Iran after existing contracts come to an end.
The Iranian economy relies heavily on oil exports
Several American firms have been able to legally work in the country in the face of a US trade embargo, through foreign subsidiaries.
Halliburton, once run by US vice president Dick Cheney, said its Cayman Island unit secured revenues of $30m-$40m (£16-£21m) from Iran in 2003.
It said it was winding down its work due to a poor business environment.
Tension has been mounting between the two nations as the US suspects Iran of developing a nuclear weapons programme.
Iran has always denied this, saying that its nuclear development programme is purely for peaceful, energy-generating purposes.
Meanwhile, a recent Iranian gas field contract won by Halliburton sparked criticism in the US.
And a federal grand jury is looking at whether any violations of the Iran trade embargo had taken place.
Halliburton chief Dave Lesar said the firm would return to the country if US legislation changed or the business climate picked up.
Halliburton saw a loss of $201m in the fourth quarter of 2004, compared to a loss of $947m a year ago, when it was hit with charges related to settlement of asbestos claims.
The company is planning to sell or float its KBR subsidiary, which is being investigated for alleged overbilling on fuel and food service contracts from the Pentagon in Iraq.