Police at one point used water cannon to disperse demonstrators trying to enter via the main entrance to the Supreme Headquarters Allied Forces Europe (SHAPE) compound near Mons in southern Belgium.

But no violence was reported in the protest action, dubbed "Get in Shape," of which the specific aim was to try to carry out "civilian inspections" inside the sprawling base.

Those arrested were due to be released later in the day, after being taken to a nearby holding centre to prevent them re-offending.

"There was a game of cat and mouse between police and demonstrators," said police spokeswoman Anne-Sophie Charle (eds: correct), putting the provisional arrest toll provisionally at 258 by late afternoon.

"There is no particular acts of violence, and no damage to public property," she added.

Security was particularly tight since the demo came a year after a similar protest at the Kleine Brogel military base in northern Belgium, which was entered by 500 people while 1,117 were arrested.

Nearly 2,200 police and troops backed with helicopters were on hand to keep control of the demonstration, whose organizers wanted to express their opposition to nuclear weapons.

"The aim of this action (was) to carry out civilian inspections on the SHAPE compound to look for proof of preparations for the use of nuclear weapons," said Fabien Rondal, spokesman for Bomspotting, the group organizing the demo.

Rondal said 39 people had entered the base -- either by cutting or scaling fences, using a variety of equipment including mattresses and rope ladders -- although most were arrested almost immediately inside.

Early Saturday morning a group of 12 -- including Belgian, British, Finnish, Swedish and US nationals -- did manage to spend over 20 minutes inside the compound before being arrested close to the main SHAPE building, he said.

Those arrested included notably a number of Belgian politicians, including the president of the Flemish-speaking Spirit party and three deputies from the national parliament.

Both police and protestors claimed success from the day's events. The police spokesman added that turnout was lower than they anticipated -- about 1,000 instead of 1,500-2,000.

According to the organizers, the protestors had intended to be arrested to highlight their cause, he said, adding that they also hoped to be charged in order to take their case to a Belgian court.

SHAPE's own security forces were not involved in dealing with the protestors, although they were on hand if anyone had penetrated further into the actual buildings themselves.

"We (were) prepared," said SHAPE spokesman Lt. Col. Hartmut Beilmann, adding that such demonstrations "are a right in a democracy."

WAR.WIRE