Fires were set Saturday at an entrance to the trade fair grounds in Hamburg, which are set to host a meeting of foreign ministers next month and the Group of 20 summit in July, German police said.

Hamburg police said witnesses reported fires late Saturday. Officers found that several garbage containers, a motorcycle, tires and part of the glass front of the entrance had been set ablaze, while stones had been thrown at the windows.

Police said Sunday that witnesses reported that around 30 to 50 people, most of them masked, were responsible. They fled before officers arrived.

Foreign ministers from the Organization for Security and Cooperation in Europe will meet at the venue next month. A claim of responsibility was posted online under the handle "noOSCE noG20."