Spanish authorities have seized more than 20,000 jihadi military uniforms bound for Islamic State (Isis) militants and al Nusra Front. The uniforms were being smuggled as "second-hand clothes" so as to ship them undetected.

Police confiscated the shipment from Spanish ports but denied they originated from the European nation. Officials said they are investigating where the shipment originally came from.

Spain's interior ministry said the uniforms were being sent to the fighters of both the IS (Daesh) in Iraq and Syria and al-Nusra Front, an al-Qaeda arm fighting in the region. Other military accessories were also found in the containers, which were intercepted in the port cities of Valencia and Algeciras. The shipment was disguised as humanitarian aid.

A statement from the ministry read: "The containers which carried the military uniforms were declared as second-hand clothes so as to not raise suspicions and be able to pass different customs inspections without any difficulty." The law enforcement agencies did not disclose the exact destination of the containers. Images of camouflage uniforms wrapped inside large bundles were released.

The Spanish police said the latest bust is connected to the earlier arrest of seven people in February. The detainees were suspected to have been providing logistical support to the extremist organisations in the conflict zones. Five of them were Spanish nationals and one of the suspects was involved in the business of importing used clothes.

"With the roughly 20,000 military uniforms and accessories, it would have been possible to equip an entire army, which would be ready to enter into combat in any of the battlegrounds which jihadist terrorist organisations have round the world," the interior ministry added.