The US Air Force has blocked from its network more than two dozen media websites, including The New York Times, that have posted secret American cables released unauthorisedly by whistleblower website WikiLeaks.

Such a decision has been taken to avoid having "classified incidents on our unclassified systems," US Air Force spokeswoman Maj Toni Tones told Fox News.

Among other sites that have been blocked include Germany's Der Spiegel, France's Le Monde, Britain's Guardian and Spain's El Pais, Tones said.

The process of blocking these websites began in August, and so far more than two dozen such websites have been blocked.

"We work diligently to use our resources in the most effective and efficient manner possible. And blocking access to the WikiLeaks' material diminishes our need to go through the labour and resource-intensive process of cleaning unclassified machines that have been compromised with classified materials," she told Fox News.

Pentagon spokesman Col Dave Lapan said that so far this restriction is only on the Air Force network and is not a Pentagon-system wide restriction.