Daniel Andreas San Diego is an alleged animal-rights extremist on the US most-wanted terrorist list since 2009 in connection with the bombing of a California biotechnology firm has been arrested in the United Kingdom. Photo: FBI

The suspect, Daniel Andreas San Diego, was arrested in Wales on Nov 25 in an operation carried out by Britain's National Crime Agency, Counter Terrorism Policing and the North Wales Police in coordination with the FBI, the FBI said in a statement.

It was not immediately clear if San Diego, who is now in detention pending extradition, has legal representation.

San Diego was charged in connection with a bomb blast at biotechnology firm Chiron Inc near Oakland, California, in August 2003. A second bomb found there was deactivated by authorities and possibly intended to target first responders. Authorities accuse San Diego of planting a third bomb at another California company a month later.

No one was injured in any of the incidents, the FBI said.

An entity calling itself the Revolutionary Cells claimed responsibility for the attacks in statements posted to a pro-animal rights website, citing the targeted firms' alleged links to Huntingdon Life Sciences, which had been criticised by animal rights activists over its use of animal testing and is now part of the firm Inotiv.

In 2004 a federal grand jury returned an indictment charging San Diego with two counts of destroying or attempting to destroy property with explosives and two counts of use of a destructive device in a crime of violence.

The FBI has said that San Diego openly expressed extreme views advocating the use of violence to achieve the goals of the animal rights movement.

FBI Director Christopher Wray said the arrest showed that no matter how long a suspect is on the run, the bureau would not stop its pursuit.

"There's a right way and a wrong way to express your views in our country, and turning to violence and destruction of property is not the right way," Wray said.