The head of U.S.-funded Voice of America says Iran's government is hoping to intimidate its citizens by banning contact with organizations such as VOA and the BBC.
VOA Director Danforth Austin says he hopes Iranians who believe in the right to free speech will continue to communicate with VOA, so other Iranians and people around the world will see what he calls the "repressive turn of events" in Iran.
He says it is a shame that Iranian officials fear the thoughts and words of their own people.
Iranian media have quoted the country's deputy intelligence minister for foreign affairs as saying the banned groups played a role in inciting post-election violence.
An Iranian legal expert, Mohammad Seyfzadeh, says banning people from talking with foreign broadcasters has no legal basis in Iran's constitution.
Other banned groups include the U.S.-based National Endowment for Democracy and a foundation run by American billionaire and philanthropist George Soros, the Open Society Institute.
On Monday, U.S. Secretary of State Hillary Clinton said Iran is showing "mounting signs of ruthless repression" in its treatment of opposition activists.
An Iranian Foreign Ministry spokesman, Ramin Mehmanparast, rejected the remarks Tuesday, saying some Western countries are following those who are "not representative of the Iranian people."
Iranian security forces cracked down on major anti-government protests late last month and arrested more than 500 demonstrators. Eight people were killed in the unrest. Authorities have since detained at least 20 high-profile opposition figures.
A U.S. Department of Defense-sponsored study released Tuesday says Iran's disputed presidential election in June has further empowered the country's Revolutionary Guards and refueled fears of a "creeping militarization" of Iranian politics and society.
The study by RAND Corporation also recommended that U.S. policy makers "take great care" in their statements regarding Iran, as not to give Iran's leadership a pretext to divert attention from domestic issues, such as the economy.
Some information for this report was provided by AP and Reuters.