Earlier on Friday, a meeting of western allies at Germany's Ramstein Air Base failed to reach a decision on delivering German-made Leopard 2 tanks to Ukraine, but Poland's defence minister said he remained optimistic that efforts to provide them would end in success.

"It is a sovereign decision by a sovereign state, which Germany is," Bauer, who is Dutch, told a news conference in Lisbon. He added that it was also important to discuss deliveries of other weapons requested by Ukraine.

"Giving away stuff now costs money but the cost for all of us will be much higher if Russia wins the war in Ukraine...We need to seriously look at what Ukraine requires and, if possible, give them what they ask for," he said, adding that that had to be done in a timely fashion.

Bauer told reporters the war was not going well for Moscow, as "none of their strategic objectives have been reached so far".

(Reporting by Catarina Demony, writing by Andrei Khalip; Editing by Jon Boyle)