An imam has been killed in a fire at a Shia mosque in the Brussels suburb of Anderlecht, in what is believed to have been a deliberate attack.
The mayor of Anderlecht was quoted by local media as saying the suspect had thrown a petrol bomb at the mosque on Monday evening.
Initial reports say the imam, 47, died of smoke inhalation and that one other person was injured.
Officials were quoted as saying a man was detained at the mosque.
"A suspect was taken into custody at the scene," police spokeswoman Marie Verbeke told AFP news agency.
"A dozen worshippers were waiting to pray when someone entered with a bag," eyewitness Azzedine Laghmish told national broadcaster RTBF.
"Inside there was a container full of petrol which he threw into the centre of the room", Mr Laghmish said.
"The fire took hold very quickly. The imam tried to put it out but he found himself stuck in a room", he added.
Local media reports say dozens of local people have gathered near the mosque. Belgian Interior Minister Joelle Milquet said she was "very shocked by the events that have occurred."