Police said a "small explosion" went off Thursday in a hotel at the Swiss alpine resort of Davos, where global political and business leaders have gathered for the World Economic Forum.
"A small explosion of unknown origin," occurred in the basement of the Morosani Posthotel in Davos, said a cantonal police spokesman. "No one was injured and material damages were minimal," he added.
Federal prosecutors would examine its cause, he said.
The organiser of the annual forum also issued a statement saying that "this morning, a small firework went off at the back of the entrance of the Morosani Posthotel".
A window had been damaged, but "the hotel is fully operational and accessible", the WEF statement added.
Swiss newspaper 20 Minutes said it had received a letter from an anti-WEF group claiming responsibility, saying they had used a "pyrotechnic device" and sugar.
Some 2,500 political and industry leaders are gathered in the small alpine village for the forum, which ends on Sunday.