DAVOS - A small blast shattered two windows but caused no injuries at a hotel near where top business and political leaders are attending the World Economic Forum, Swiss police said Thursday.

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The explosion happened in a storage room of the Posthotel Morosani shortly after 9 am local time (0800 GMT) Thursday, regional police spokesman Thomas Hobi told the AP. He said federal prosecutors are investigating whether the blast has a criminal origin.

The Forum said in a statement a firework in the back of the hotel was to blame. The hotel did not comment.

The hotel is just over a mile (around 2 kilometers) from the main venue of the annual gathering in the Alpine ski resort of Davos.

There was little disruption to the hotel afterward and its activities beyond an increased security presence at the hotel's entrance. Guests, journalists and others were going inside.

A Forum-related lunch focusing on organized crime, called "Criminals Without Borders" went on as scheduled at the hotel at noon, with speakers including Colombian President Juan Manuel Santos and Robert Wainwright, the director of Europol, or European Police.

There is tight security at the World Economic Forum as left-wing groups plan to hold a protest this weekend against the annual meeting of political and business leaders and social activists.

Anonymous flyers circulated at a demonstration last week in the northeastern Swiss town of St. Gallen urged activist to "Smash (the) WEF."

The flyer says: "Let us fight together against the unbearable propaganda of capitalism."

In previous years violent activists have stayed away from the chic ski resort and staged violent demonstrations elsewhere in Switzerland instead.