BRUSSELS (Reuters) - Around 100 anti-war protesters were arrested trying to force their way into NATO’s headquarters in Belgium on Saturday, police said.

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Police in riot gear and on horses clashed with over 500 activists from across Europe -- opposed to military action in Iraq and Afghanistan and the use of nuclear weapons -- outside NATO’s Brussels hub.

Water cannons were used to prevent most of the protesters from gaining entry to the large security compound situated on the outskirts of the Belgian capital and close to Brussels national airport.

At least one protester was taken to hospital with serious injuries after falling on barbed wire, a police spokeswoman said. “We have arrested over 100 and they are being taken to court to be dealt with swiftly.”

A NATO official said the compound had not been breached.

“Demonstrations are a feature of democracy. All we hope for with any such protest is that it is done in a peaceful and safe manner,” the official told Reuters.

NATO is a security and defense alliance of 26 countries from North America and Europe with forces in Iraq, Afghanistan, Kosovo and Darfur.

Organizers of Saturday’s “NATO Game Over” protest say without the military organization, the wars in Iraq and Afghanistan would not be possible. They also oppose the use of nuclear weapons.

“Today is close to the fifth anniversary of the war in Iraq and we are protesting against NATO’s involvement and in particular European countries which are allowing themselves to be used as military hubs,” anti-war campaigner Hans Lammerant told Reuters.

“NATO has 350 U.S. nuclear weapons deployed in Germany, Italy, Belgium, the Netherlands, Britain and Turkey. According to international humanitarian law these weapons are illegal.”