This undated and unlocated handout picture released by Spanish Policia Nacional on March 14, 2017 shows an arsenal with more than 10,000 weapons seized by Spanish police.
A huge cache of weapons was impounded by the Spanish police in January when they cracked down on an organised syndicate in Bilbao, the largest city in Basque country.
Police had seized 10,000 assault rifles, machine guns, pistols, revolvers, and 400 shells and grenades, the BBC reported.
Police also recovered 80,000 euros ($85,000) during the raid.
Five people were arrested when a joint police team from Madrid, Valencia and Gerona busted the crime group specialising in reactivating deactivated firearms.
The syndicate used a sports shop as a front to do the illicit business. They bought the weaponry through auctions and legal channels.
They found loopholes in the European bloc to divert legal firearms into the black market, according to Europol.
A deactivated gun is a firearm that has been manipulated for it to be non-lethal. One cannot shoot rounds from that firearm.
Reactivating imitation firearms has been a major concern for police in Europe as there are fears that they eventually land up with terror outfits.
For instance, the weapons used for the deadly attack on Charlie Hebdo staffers last year were allegedly acquired from Slovakia.
Police said acquisition of such firearms had visibly spiked since 2014.