Spanish police have seized 20,000 military uniforms bound for Islamic State and al Nusra Front fighters.
They said the haul was "enough to equip an entire army" and had been declared second-hand clothes in an attempt to fool customs officials.
The military uniforms were discovered in three shipping containers in the eastern ports of Valencia and Alicante last month, as officers uncovered an operation to smuggle arms to jihadists.
Police said in a statement: "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."
One of the seven people arrested was a man who dispatched "military material, money, electronic and transmission material, firearms and precursors for making explosives" to Syria and Iraq via a company.
This was shipped out to the terrorist groups under the guise of humanitarian aid.
It comes as a partial ceasefire in Syria entered its seventh day.
However, Islamic State and al Nusra Front – an al Qaeda affiliate – are not covered by the cessation.