The US military is developing software that will let it secretly manipulate social media sites such as Facebook and Twitter by using fake online personas to influence internet conversations and spread pro-American propaganda.

A Californian corporation has been awarded a contract with United States Central Command (Centcom), which oversees US armed operations in the Middle East and Central Asia, to develop what is described as an "online persona management service" that will allow one US serviceman or woman to control up to 10 separate identities based all over the world.

The project has been likened by web experts to China's attempts to control and restrict free speech on the internet. Critics are likely to complain that it will allow the US military to create a false consensus in online conversations, crowd out unwelcome opinions and smother commentaries or reports that do not correspond with its own objectives.