A number of arrests were made when disorder broke out at an anti-arms protest in East Sussex.
Activists forced their way into the grounds of EDO MBM Technology in Brighton on Wednesday and caused damage to cars and windows.
Police said an apparently lawful event had been "hijacked" by people intent on violence.
About 350 protesters had earlier gathered at the Level park area to mark four years of campaigning against EDO.
Violence 'unjustified'
Paul Pearce, city commander of Brighton and Hove Police, said the level of violence was not justified.
"As with previous causes, apparently lawful protest has been hijacked by people who are intent on committing violent criminal offences," he said.
"Any doubts that the campaign has attracted such people have been dispelled today," he added.
The Brighton-based campaign group Smash EDO said the protest showed its campaign was "still going strong".
The group was formed in 2004 and stages regular protests at the EDO MBM grounds.
EDO MBM were not available for comment.
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