Several choirs sing together in support of peace in Ukraine, in the centre of Madrid, on March 26, 2023. (AFP)
Madrid announced in February it would send the German-made 2A4 Leopards to Ukraine after they underwent repairs.
The tanks have not been used in years and were in storage at a military base in the northeastern city of Zaragoza.
Robles said the Spanish army was testing the six tanks before delivering them to Ukraine after Easter Sunday on April 9.
Spanish Prime Minister Pedro Sanchez announced during a visit to Kyiv on February 23 that Spain could send an additional four Leopard tanks to Ukraine.
"These four supplementary tanks need to be repaired," Robles said, without indicating when they could be delivered to Ukraine.
Earlier this month 55 Ukrainian soldiers wrapped up a four-week training course in Spain on how to operate the Leopard tanks Western allies have promised Ukraine.
Britain and Germany said Monday they have delivered Western heavy tanks to Ukraine, providing a key infusion of armoured firepower.
The tanks -- long an item on Ukraine's military equipment wish list -- have arrived in time for an expected spring offensive by Ukraine's forces.