The latest of 10 attacks took place at the weekend in the Belgian city of Genk. The fast food restaurant was seriously damaged by fire.

No-one has been hurt in the campaign of violence, but the authorities believe they face a serious threat.

A security force spokesman said they were investigating a possible connection through the Internet with the Animal Liberation Front in the UK.

The most extreme and macabre incident so far involved digging up a body which was then left on a doorstep of a McDonalds branch.

Protest against killing of animals

In statements to the local press, animal rights activists have admitted responsibility for the arson attacks.

They said they were protesting against the killing of animals and the destruction of the tropical rain forests to make way for cattle breeding.

A dead body was left on the doorstep of a McDonald's branch

The Animal Liberation Front in Britain reported the attacks on its website and refused to condemn them.

"It has only just begun in Belgium, but now that it has started, it will continue as long as animal abuse continues. The people concerned are Belgian citizens who are tired of the law failing the animals," spokesman Robin Webb told the BBC by phone..

Fears of escalation

The authorities are now seriously alarmed. The Belgian security service, the equivalent of MI5 in Britain, has taken charge of the investigation.

"At the moment, there are no casualties, but we can't exclude it. If people begin with terrorist attacks, where will it end? We have to investigate this problem," says Jean-Baptiste de Smet from Belgian security forces.

BBC Europe Correspondent David Shukman says the security forces find the connection to Britain via the Internet very hard to police.

In Britain, Scotland Yard is setting up a special unit to combat so-called animal terrorism.