Belgian prosecutors said on Wednesday (5 July) that four people had been detained after automatic weapons were found in house searches in Brussels as part of a counter-terrorism investigation overnight.
"We fear they may feel cornered. We therefore fear there could be the same reaction as on March 22 (2016)", said. In October 2016, two members were convicted of belonging to a terrorist group.
They had plans to carry out an attack, Flemish-language broadcaster VRT said, citing sources.
Police officers of an anti-terrorism unit and of French intelligence agency (DGSI) patrol in a street on Wattignies, northern France, during the operation to pick up a man on suspicion of links to the Kamikaze Riders, an ISIS-related group.
Police found Kalashnikovs, bullet-proof vests and ammunition in raids on two garages and four homes in the Brussels' Anderlecht district.
A source close to the probe said the two men in custody are brothers of Said Saouti, a member of the Kamikaze Bikers club who was jailed for six years in 2016 for recruiting people to jihadist organisations and supporting the Islamic State (IS) group on social media.
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There was no information on a possible target but the police decided not to wait any longer. "In all, four persons were arrested and taken in for questioning", prosecutors, adding the raids were linked to the Kamikaze Riders, which has been implicated in terror offences.
They also found explosive materials in a raid on his home in Molenbeek, a Brussels district where numerous jihadists who carried out the Paris and Brussels attacks grew up and found shelter.
Formed in 2003, they are suspected of links to ISIS and foiled attacks in Brussels in 2015.
Belgian authorities say at least one man is on the run a day after police arrested two suspected militants.
They were originally suspected of plotting an attack similar to the November 2015 carnage in Paris that left 130 people dead.