A car drove at high speed into a group of Belgian carnival performers who were preparing a parade early on Sunday, killing six people and seriously injuring 10 others, authorities said.
"At this stage, there are no elements to suggest that the attack had a terrorist motive," prosecutor Damien Verheyen told a news conference.
Police denied media reports the car was involved in a high-speed chase.
The incident occurred in the southern Belgium village of Strepy-Bracquegnies at around 0400 GMT.
Jacques Gobert, mayor of the neighbouring town of La Louviere, said between 150-200 people were gathered to get ready for the annual folklore parade, involving costumes and drums, when the vehicle appeared.
"A speeding car drove into the crowd ... The driver then continued on his way," said Gobert.
The two people driving the car, which was later intercepted, were detained. Police said they were local people in their 30s and were not previously known to police.
Belgium has sought to root out people suspected of militant links over the past seven years. A Brussels-based IS cell was involved in attacks on Paris in 2015 that killed 130 people and on Brussels in 2016 in which 32 died.


Nepal to rebuild early-warning system on China border after deadly flood, sources say
US House passes bill to crack down on university boycotts of Israel
Kuwait air defences deal with Iranian missile, drone attacks
Spain's PM Sanchez says no evidence Morocco orchestrated Ceuta border surge
Two Palestinian teens killed in West Bank raid by Israeli settlers, army
Latest Indonesian free meal poisoning outbreaks affect 800, lawmaker says
Chinese students marooned in floods unleashed by Typhoon Saudel's rains
US and Iran exchange attacks as lull in war appears over
