The Iranian government has banned its citizens from having contact with 60 organisations including the BBC, Voice of America and Human Rights Watch.
The deputy intelligence minister in charge of external affairs said the 60 blacklisted groups were suspected of being involved in efforts by Western governments to topple the Islamic regime as part of a "soft war" and that it is now an offence to communicate with them.
"Any kind of contact by individuals or legal entities with those groups involved in the soft war is illegal and prohibited," he said. Iranian state media did not give his name.
The blacklisted organisations include the opposition website Rahesabz and the US-funded Radio Farda as well as American-based pro-monarchist satellite channels, Israeli public radio and the outlawed rebel People's Mujahedeen.
The minister also called on the public to avoid "irregular contacts with embassies or foreign nationals or centres linked to them".
"Citizens should be alert to the traps of the enemies and co-operate with the intelligence ministry in protecting the nation and neutralising the plots of foreigners and the conspirators," he said in allusion to opposition sympathisers who have held repeated protests over the past seven months following the country's dispuite presidential election whiuch returned Mahmoud Ahmahdinejad for a second term in office.
Other blacklisted groups included the Brookings Institution, George Soros's Open Society Institute and the Washington-based National Endowment for Democracy.
On Monday, Heydar Moslehi, Iran's intelligence minister, said several foreign nationals had been arrested at anti-government protests last month that left at least eight people dead.
"They had entered Iran only two days before Ashura [a Shia religious festival]. Their cameras and equipment have been seized," he said, without specifying how many had been arrested or their nationalities.
In late November, the Supreme Leader, Ayatollah Ali Khamenei, said Iran was in the throes of a "soft war" with its enemies abroad, who he claimed were fomenting the street protests. The claim has become a mantra of regime officials, who are sensitive to criticism from Western leaders and have accused them repeatedly of supporting the opposition.