RAMSTEIN AIR BASE, Germany: Ukrainian President Volodymyr Zelenskyy said on Friday there was 'no alternative' but for the West to give heavy tanks to his country, as Germany failed to commit its sought-after Leopard vehicles to a possible spring offensive by Kyiv.

A United States-led meeting of some 50 allies of Ukraine came through with billions of dollars' worth of military hardware, including ample armored vehicles and munitions needed to push back Russian forces.

But Zelenskyy stressed he needed battle tanks on top of that, as US Secretary of Defense Lloyd Austin said Ukraine was expected to mount an attack against dug-in Russian troops in the coming weeks.

'We have a window of opportunity here between now and the spring ... whenever they commence their operation, their counteroffensive,' Austin said at the meeting at Ramstein Air Base in western Germany.

Zelenskyy urged the group in a video address to 'speed up' arms deliveries and stressed Germany's Leopard tank was a primary need.

'Every day we make it more obvious that there is no alternative, that a decision about tanks must be made,' he said.

Expectations had grown ahead of the Ukraine Contact Group meeting, a grouping of arms providers led by Austin, that Germany would at least agree that other countries operating Leopards would be permitted to transfer them to Kyiv's army.

The reasons for Germany's reticence remained unclear, as the United Kingdom has agreed to send 14 of its Challenger 2 tanks to Ukraine.

German Defense Minister Boris Pistorius told reporters: 'We still cannot say when a decision will be taken, and what the decision will be, when it comes to the Leopard tank.'

Austin defended Germany against criticism that it was not doing enough to help Kyiv.

'We could all do more,' Austin said, emphasizing that Berlin was a 'reliable ally.'