SPANISH cops have seized an astonishing arms haul of over 10,000 firearms and grenades.

The jaw-dropping cache of machine guns, assault rifles and rifles was uncovered by police from Madrid, Girona, Valencia and Bilbao in a joint operation.

DEADLY: Weapon haul found by Spanish cops
DEADLY: Weapon haul found by Spanish cops

The weapons belonged to an organised criminal gang, who used an illegal workshop near Bilbao to store and reactivate the weapons.

Five people have been arrested following the operation, which also uncovered €80,000.

Criminals are believed to have purchased the weapons through auctions before reactivating them.

Police say they were being sold throughout Spain, France and Belgium and could easily have ended up in the hands of terrorists.

The gang had used a sports shop as a front to sell the weapons.

Reactivating deactivated weapons is one of the most popular ways for European criminals to access illegal weapons.