US lawmakers expressed support for the Iranian people's right to free speech and peaceful protest in resolutions adopted on Friday.
The moves come as tens of thousands of people in Iran have taken to the streets in demonstrations against last week's election results. Some of the protests have turned bloody, and there have been fatalities.
Iran's President Mahmoud Ahmadinejad was declared the winner with more than 60 percent votes, but opposition candidate Mir-Hossein Moussavi has alleged fraud and called for a complete rerun of the election.
The US House of Representatives adopted a resolution that "affirms the universality of individual rights and the importance of democratic and fair elections".
The resolution also "condemns the ongoing violence against demonstrators by the government of Iran and pro-government militias".
The Senate approved a similar resolution that "supports the Iranian people as they take steps to peacefully express their voices, opinions, and aspirations".
US President Barack Obama has made similar comments in the past few days, but has walked a fine line between supporting peaceful protests while not appearing to meddle in Iran's affairs.
The administration has said that Iran should allow freedom of expression and halt violence against the demonstrators, but has stopped short of suggesting that the election results were fraudulent.
Critics charge that Washington has not done enough to back the opposition protests. Some Republicans had pushed for the resolutions to be more forceful.