A small explosion broke some windows but caused no injuries at a hotel used by leading business and political figures attending the World Economic Forum, authorities said Thursday.

Thomas Hobi, a spokesman for the local Davos police office, told Xinhua that the blast in the basement of the Posthotel Morosani in the Swiss Alpine town of Davos broke several windows.

Forum organizers said in a statement that the explosion was caused by a firework.

The Swiss federal prosecutors office said in a statement that it is investigating the incident but provided no further information.

An eyewitness told Xinhua that the blast was caused by a group of WEF protestors.

An anonymous posting on the website indymedia.ch claimed responsibility for the attack on the Posthotel Morosani, saying it was directed at Swiss government officials and senior executives of Swiss bank UBS staying at the hotel. Its authenticity couldn't immediately be confirmed.

The incident occurred on the day French President Nicolas Sarkozy, British Deputy Prime Minister Nick Clegg and former U.S. President Bill Clinton were due to take the stage at the annual gathering.