Trump's looming return to power after triumphing in elections against Democrat Kamala Harris has sent shockwaves through the EU as Russia wages war against Ukraine on its border.

The volatile former reality TV star during his first term in power lambasted Washington's European allies in NATO to spend more on defence.

On the campaign trail, Trump rattled Europe by saying he would encourage Russia to "do whatever the hell they want" with alliance members not spending enough.

Former Lithuanian prime minister Kubilius -- who needs to be confirmed by EU lawmakers in his new role -- pointed out that European countries had ramped up their budgets since Russian President Vladimir Putin invaded Ukraine in 2022.

"We need to spend more, but not because that is a demand from President Trump, but because of Putin, because of the threat of Putin," Kubilius told a hearing at the European Parliament.

Kubilius said that "recent intelligence assessments suggest Russia may test the resolve of the EU or NATO by the end of this decade."

"That is why we must urgently enhance the EU's readiness for potential military aggression. This is the way we can deter it," he said.

"We do not want war. We want peace. Therefore, we must become ready for defence."