NATO Secretary General Mark Rutte on Thursday called for the U.S. to continue supplying Ukraine and said Europe would pay the bill.

Speaking at an event at the World Economic Forum in Davos, the NATO chief said the alliance must invest more in defence, ramp up defence industrial production and take on a bigger share of spending on help for Ukraine.

"On Ukraine, we need U.S. also to stay involved," Rutte said.

"If this new Trump administration is willing to keep on supplying Ukraine from its defense industrial base, the bill will be paid by the Europeans, I'm absolutely convinced of this, we have to be willing to do that," he added.

The secretary general's comments came after U.S. President Donald Trump said earlier this week that the European Union should be doing more to support Ukraine.

In Davos, Rutte also said it was vital Russia did not win as it could result in Russian President Vladimir Putin 'high fiving' the leaders of North Korea and China.

"We really have to step up and not scale back our support for Ukraine," the NATO chief said.

"The frontline is moving in the wrong direction," he said.