AMSTERDAM - A district courthouse in Amsterdam's central business area was badly damaged by an explosion overnight, Dutch police said on Wednesday.

"We cannot say what kind of explosion it was. The investigation is ongoing," a police spokeswoman said.

Dutch radio reported the damage may have been caused by a grenade. No one was injured, police said. "Lots of windows on different floors are damaged," the spokeswoman said.  

The courthouse was the venue of the high-profile trial of populist politician Geert Wilders. He was acquitted of inciting hatred of Muslims in June.  

"A few windows are damaged, on various floors. The damage is visible from the outside. The court cases will continue today," said Yudra Poel, a court employee.