Spanish police have arrested two people on suspicion of weapons trafficking and seized a stash of firearms, explosives and ammunition.

An investigation began when police detected that someone was allegedly selling weapons for less than their normal sale price, according to a statement.

A surveillance operation led to five house searches in and around the eastern port city of Castellon and the arrest of two Spaniards, aged 48 and 60.

The seizure includes 25 firearms, 20 kilograms (44 pounds) of explosives and 30,000 bullets of varying calibers, including illegal subsonic, hollow-point ammunition.

Sunday's statement says police are investigating if the arms haul has been used in criminal acts or formed part of an international smuggling operation.