Washington released its annual religious freedom report on Tuesday, with Secretary of State Rex Tillerson criticising Bahrain, China, Iran, Pakistan, Saudi Arabia, Sudan and Turkey.
Tillerson charged that Iran had used "vague apostasy laws" to execute 20 members of religious minorities over the past year.
"Iran considers it an unrealistic, baseless, unfounded and biased report which has only been made with the intention of certain political gains," foreign ministry spokesman Bahram Ghasemi hit back on the ministry's website.
He said Washington should focus on improving its own record of discrimination, particularly regarding its Muslim population.
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"Muslims in America face violent and discriminating actions on a daily basis by state bodies like the police and security forces."
The US report said the Iranian government "continued to harass, interrogate and arrest Bahais, Christians, Sunni Muslims and other religious minorities and regulated Christian religious practices closely to enforce the prohibition on proselytising."
The government in Tehran also used anti-Semitic language and promoted Holocaust denial, it charged.