The man, said to be a friend of one of the March 2016 Brussels bombers, was arrested last night in a huge security operation that shut down part of central Brussels.
"The prosecutor can confirm that M.A. Has been released," prosecutor's spokesman Denis Goeman said, identifying the man only by his initials.
"According to the latest information, no element that could justify detention or an arrest warrant was found," he added.
Investigations showed that the gas canisters appeared to be for domestic use as the suspect had claimed, prosecutors said.
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A Belgian court sentenced the man in 2016 to five years in jail, partly suspended, for taking part in the activities of a terrorist group.
He was a "close friend" of Najim Laachraoui, one of two Islamic State-linked suicide bombers who blew themselves up at Brussels Airport on March 22 last year, a source close to the inquiry said.
The suspect had also tried to go to Syria twice, the source added.
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