The 55 Ukrainian trainees arrived mid-February in Spain and are scheduled to fly to Poland on Wednesday as they start to make their way back to Ukraine and the frontline, ministry sources said.

They have been training 12 hours a day, six days a week, at a Spanish military base in the northeastern city of Zaragoza, Captain Contreras, who declined to give his first name, told reporters Monday during a tour of the San Gregorio training military camp.

On Saturdays, they trained only in the mornings, said the officer, who headed the Spanish military unit charged with training the Ukrainian soldiers.

"They are very motivated," he added. "They have a strong desire to learn and are eager to return and contribute to the defence of their country."

The soldiers ranged in age from 21 to 60 years and all had previous battle tank experience, he said.

"While battle tanks are different, there are many systems that are similar, and that made things much easier," Captain Contreras commented.

The group received technical and tactical training and will return to Ukraine "with a very acceptable knowledge" of the German-made Leopard 2A4 tanks, he added.

Part of the European Union's military assistance to Ukraine, the training included both exercises on simulators and actual Leopard 2 tanks.

Captain Contreras said his team gave the group as little theoretical training as possible, "because they prefer practical training, as you can understand."

The soldiers operated several tanks on a field at the miliary base on Monday, kicking up a trail of dust behind the vehicles.

Spanish Prime minister Pedro Sanchez said during a visit to Kyiv in February that Spain would be sending six Leopard 2A4 tanks immediately and hoped to send four more later.

Germany initially resisted the pressure from allies to authorise the move, but early this year agreed to send its own Leopards and greenlighted the deliveries from other countries.

The Ukrainian soldiers praised the "superior capacities" of the tanks from the ones they had used before and those they faced from the Russian side, Captain Contreras added.