Brussels - Hundreds of anti-nuclear demonstrators were arrested on Monday after storming a Belgian Air Force base where they believe US nuclear bombs are stored, organisers and witnesses said.

 After marching to the perimeter of the Kleine Brogel base, the demonstrators broke down a wire fence and streamed on to the base, witnesses said.

 Police and military personnel, who were vastly outnumbered by the demonstrators, tackled some of them and put plastic handcuffs on them.

 Eventually the demonstrators sat down, awaiting arrest.

 Kleine Brogel, about 100km northeast of Brussels, has been the target of demonstrations for several years because anti-nuclear activists believe US nuclear bombs are stored there, although the Belgian government has never confirmed this.

 Hans Lammerant, a spokesman for Forum for Peace Action, one of the groups organising the protest, said that 1 500 people had taken part in the march and between 800 and 900 people had entered the base.

 "They are arresting everyone. They are sitting in big groups on the landing strips. The idea is to get arrested because we want to have a trial about nuclear weapons," he told Reuters by telephone.

 "In our opinion they are illegal weapons, so they can never be used without breaking international humanitarian law," he added.

 Flemish television said between 300 and 400 people were arrested.

 A police spokesman could not immediately be reached for comment and a Defence Ministry spokesman had no information.

 There were no reports of injuries.

 The organisers said in a statement they believed that nuclear weapons were illegal following 1996 advice from the International Court of Justice in The Hague that the use or threat of nuclear weapons in war should be outlawed.