"The crimes of Saddam, his cronies and his international supporters go beyond the national Iraqi framework and have an international dimension," said a statement signed on Wednesday in Tehran by 256 deputies in the 290-seat Majlis.
"He should be judged publicly and before an international court comprising independent judges, among them Iraqis and Iranians," it said.
The statement also hit out at last week's hearing in Iraq, which it described as "not free, closed-door, subject to censorship and under the control of the occupying forces".
Iran announced on Sunday that it had prepared a complaint against Saddam Hussein for his September 1980 attack on Iran and use of chemical weapons, and will soon file the dossier with the Iraqi tribunal putting the former president on trial.
"The crimes of Saddam, his cronies and his international supporters go beyond the national Iraqi framework..."
Saddam Hussein's 1980 land grab - which sparked the catastrophic 1980-1988 Iran-Iraq war - did not figure on the original list of charges. Neither did his extensive use of chemical weapons against Iranian forces.
According to official figures, Iran has 45,000 registered war veterans with chemical injuries who cost the regime around $20 million a year to support.
Iran has also alleged Iranian prisoners were tortured and executed in captivity.
The head of Iran's new conservative-held parliament, Ghulam-Ali Haddad Adel, has also denounced the trial as "American".