Six Leopard 2A4 tanks destined for Ukraine left Spain by ship Friday, according to a naval monitoring website, part of Western military aid for Kyiv's fight against Russia's invasion.

The German-made Leopard tanks and armored personnel carriers were driven onto a cargo vessel, Reuters witnesses said. The ship will go to Poland and the hardware transferred to Ukraine, which is expected to launch a spring counteroffensive. It was unclear when the equipment would arrive.

Spanish Defense Minister Margarita Robles said this month that Spain will send 10 Leopard 2A4 tanks. The military is repairing the remaining four. Spain has also trained 40 tank crew members and 15 mechanics.

Ukraine has been reliant on outdated Soviet-era tanks and appealed to the West for modern battle tanks, saying they are critical to its ground capabilities.

The U.S. in January promised 31 of its Abrams tanks while Germany committed Leopard tanks. NATO countries have promised to send 48 Leopard 2 tanks to Ukraine.