A US report which critics the treatment of religious minorities in Iran has been dismissed by the Islamic republic as "political" and "lacking legal proof".

The US State Department stated in its annual report on religious freedoms that the treatment of religious minorities in Iran had worsened since Mahmoud Ahmadinejad was elected as president in June 2005.

The report cited instances of abuse, including imprisonment and harassment, inflicted on particularly Zoroastrians, Jews and Christians - members of the only officially recognised minority religions in the Islamic state, AFP reported.

The claims in the US report have been hotly denied in a statement from foreign ministry spokesman Mohammad Ali Hosseini.

"America is not credible to judge on human rights, and obviously the report... pursues a US foreign policy agenda and is of no value," said Hosseini.

"America has no credit in the world, with the sinister and medieval prisons of Guantanamo and Abu Ghraib, concealing detention facilities in Europe as well as footage of torture by American guards," Hosseini said.

"The American government had better put an end to the banal, useless game of issuing reports and lists on human rights violators," he added, branding the report "political" and "lacking legal proof."

The "Report on International Religious Freedom" released to Congress comes ahead of the annual announcement blacklisted countries - countries "of particular concern" to the US that are also subject to US sanctions.

Iran came top of last year's list, which also featured China, Eritrea, Myanmar, North Korea, Saudi Arabia, Sudan and Vietnam as the world's worst oppressors of religious freedom.