Russia's annexation of four Ukrainian territories makes it "much more difficult, nearly impossible for the war to end," the EU's foreign policy chief Josep Borrell told Spain's RTVE television on Saturday.

"Russia is losing" the war, he said in separate comments to a forum in Spain. It "has lost in moral and political terms," but "Ukraine has not yet won."

He said Europe has constructed "a garden" that is "surrounded by the jungle".

"If we don't want the jungle to invade the garden... we need to get involved," he said, calling for the EU to beef up its military arsenal.

"This is necessary and indispensable for survival," he said.

The European Union has steadfastly backed Ukraine after Russia invaded its pro-Western neighbour.