NATO Secretary General Mark Rutte has warned that Russian President Vladimir Putin wants to "wipe Ukraine off the map" and may come after other parts of Europe. It urged Europeans to pressure their governments to increase defense spending, they said world media.

"It is time to switch to wartime thinking," Rutte told security experts and analysts at the Carnegie Europe think tank in Brussels.

He said people should brace themselves for the prospect that Russia could try to use "swarms of drones" in Europe.

NATO leaders have agreed to end defense cuts that began when the Cold War ended after Russia annexed Ukraine's Crimean Peninsula a decade ago, moving toward spending 2% of GDP on their military budgets.

But after Russia invaded Ukraine almost three years ago, they agreed that the 2% target should be the minimum for defense spending.

US President-elect Donald Trump, who takes office on January 20, has threatened that the US will not defend "delinquent" countries that do not spend enough on their defense.