US authorities, participating in an international investigation, have shut down 20 independent news websites run by the Independent Media Center (Indymedia) by seizing two UK-based web servers.

Last Thursday morning, a US federal order was issued to San Antonio-based web hosting provider Rackspace requesting the computer equipment, according to the Indymedia website. Rackspace was hosting the Indymedia Web servers in London.

Rackspace said in a statement that the order was issued under the Mutual Legal Assistance Treaty (MLAT). The treaty allows mutual cooperation between countries in investigations such as international terrorism, kidnapping and money laundering.

It said the investigation was not initiated in the USA. Some local press outlets reported that the investigation originated in Europe.

"Rackspace is acting as a good corporate citizen and is cooperating with international law enforcement authorities. The court prohibits Rackspace from commenting further on this matter," the statement said.

Officials from the Home Office in the UK and the US FBI could not immediately be reached for comment.

Indymedia said it did not know why the servers had been seized, as the subpoena was issued to Rackspace and not to Indymedia. The group, which describes itself as an international media network covering social justice issues, said it "insists that the servers are returned”.

The Indymedia site in the UK was restored because it was backed up on another server, the group said, though other sites remained offline today. The websites affected by the seizure are located in 17 countries.

Indymedia called it "ironic" that the action came just before it was to participate in the European Forum on Communications Rights being held alongside the European Social Forum, covering issues such as electronic civil liberties and community media.