US troops are going to be allowed to use social networks such as Twitter and Facebook after a Pentagon review found that the benefits of social media outweigh security concerns.

The decision, which comes at a time of growing concern over cyber-security, applies only to the US military's non-classified network.

But it could mean big changes for large portions of the US armed forces, including the Marines, which had selectively banned social media on work computers.

Social media are increasingly important for the US military. Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, has a Twitter feed with more than 16,000 followers.

Defence Secretary Robert Gates, 66, has said he wants to use social networking to help the Pentagon interact with US soldiers, many of whom are in their early 20s.