Belgian police held four people Monday over the 2015 attack on a high-speed Thalys train to Paris in which an Islamic State extremist shot and seriously wounded a passenger before being overpowered.

Police raided six properties around Brussels and "four people were taken in for questioning", Belgian prosecutors said in a statement.

An investigating judge will decide later what further action to take against the detainees.

A bloodbath was only narrowly averted on the train from Amsterdam to Paris when quick-thinking passengers including two off-duty US servicemen subdued gunman Ayoub El Khazzani -- who was armed with a Kalashnikov, a pistol and a box-cutter knife -- as he opened fire.

Two of Monday's raids were in the gritty Brussels district of Molenbeek, which has gained notoriety as a hotbed of international jihadists after the Brussels bombings in March 2016 and the Paris attacks in November 2015.

"No explosives nor weapons were found" during Monday's raids, prosecutors said.

Khazzani, a Moroccan who fought for IS in Syria, has told investigators he was acting on the orders of Abdelhamid Abaaoud, one of the organisers of the November 2015 Paris attacks, whom he met in the war-torn Middle Eastern country.

Source: AFP