The US Treasury Department has eased sanctions on Iran, Cuba and Sudan to allow exports of web tools and online services. US Secretary of State Hillary Clinton says the move is designed to support the "right of free expression" without hindrance from repressive regimes.

US technology firms have not been supplying these countries with software needed for social networking, blogging, chatting, instant messaging or photo/video-sharing for fear of violating sanctions. Iran, Cuba and Sudan are all on a US blacklist.

In the case of Iran, Ms Clinton referred to the role of applications and websites such as Facebook, Twitter and YouTube in recent political events and opposition demonstrations. She said the end of the export ban on web tools would allow Iranians "to communicate without being blocked by their own government".

It is not clear whether the three countries in question will impose their own restrictions on the social networks. Earlier this year, Ms Clinton said the US would support the development of new tools to enable internet users to circumvent censorship imposed by restrictive regimes.