The UK-based servers of media company Indymedia have been returned to the London datacentre of hosting firm Rackspace .

But Indymedia is still none the wiser about why the US Federal Bureau of Investigation (FBI) seized them in the first place.

It had been using the seized servers to run independent news sites and radio streams dedicated to social activist groups, as well as open-source projects, from all over the world. Data and services in 17 countries were affected.

Indymedia says it is working with the US pressure group, the Electronic Frontier Foundation (EFF) to mount a legal challenge to the actions.

'The FBI can't pull the plug on more than 20 news web sites - our modern printing presses - based on a secret proceeding at the request of a foreign government. This is a flagrant violation of the First Amendment,' said Kevin Bankston, EFF attorney.

'As far as the [US] Constitution is concerned, Indymedia has the same rights as any other news publisher. The government can't shut down the New York Times, and it can't shut down Indymedia.'

Reports of an FBI spokesperson confirming the subpoena to seize the servers was issued at the request of Italian and Swiss authorities, and have been circulating since the US authorities would only confirm the investigation originated outside of the US.

This would confirm Indymedia's first suspicions that the sting could have been connected to several recent FBI requests to remove photos of undercover Swiss police taken at the G8 summit in Evian last year from one of its sites.

While there have also been reports that the Italian government had been investigating a local Indymedia group for alleged terrorist involvement.