A gunman has shot dead three people at the Jewish Museum in the Belgian capital Brussels, officials say.
A fourth person was seriously wounded, emergency services said.
The attacker arrived by car, got out, fired on people at the museum entrance, and returned to the vehicle which then sped away, Belgian media report.
Foreign Minister Didier Reynders, who was one of the first people to arrive at the scene, said he was shocked by the attack.
"I heard bursts of gunfire, rushed here and saw the bodies on the ground," he said.
The gunman arrived at the museum at around 15:50 (13:50 GMT) carrying a backpack and opened fire before fleeing in an Audi, local media report.
They say one eyewitness may have made a note of the number plate and given it to police.
Brussels Mayor Yvan Mayeur said three men and a woman had been caught up in what he thought was probably a "terrorist act". "It's clearly extremely serious," he was quoted as saying, "and on the Jewish Museum too, which isn't a coincidence".
Eyewitness Alain Sobotik told AFP news agency he had seen two bodies in the lobby of the museum.
One was "a young woman with her head covered in blood", he said. "She was holding a leaflet and looked like a tourist."
Interior Minister Joelle Milquet said everything pointed to an anti-Semitic attack.
A number of people were treated for shock after the shooting in the central Sablon area of the city.
Prime Minister Elio Di Rupo expressed his condolences and support for the victims' families.