More than 10,000 assault rifles, 400 howitzer shells, grenades, and anti-aerial machine guns — likely intended for sale to terrorists and criminals — have been seized in a joint raid by Spanish police and Europol.

Video footage released by Europol on Tuesday shows the massive cache of weapons, which the Spanish National Police seized in Bilbao, Cantabria and Gerona in January as part of operation Portu, which was supported by Europol. The haul was so great it took weeks to catalogue.

The European policing agency said in a statement that there was a "significant risk" of the weapons "being acquired by organised crime groups and terrorists."