Davos, Switzerland (CNN) -- There was a "little explosion" Thursday at the Post Hotel Morosani in Davos, Switzerland, which is hosting the high-powered annual World Economic Forum this week, police there said.

Fon Mahturos, a WEF spokesman, said "a small firework went off at the back entrance" of the hotel.

Former U.S. President Bill Clinton is scheduled to attend a party Thursday night at the hotel, one of the most prestigious in Davos.

One window was damaged, and police are investigating. The hotel is fully operational and accessible, Mahturos said.

There were no reports of injuries.

Someone at the hotel for a meeting said the blast was so minor that most guests and visitors would not know that anything had happened.

Swiss media say an anti-WEF group had threatened in an e-mail to attack the hotel with fireworks.

Swiss newspaper La Tribune de Geneve says the hotel is being used by the Swiss government during the forum.

CNN's Erin McLaughlin contributed to this report.