NATO Secretary-General Mark Rutte has warned the United States and Europe against any temptation to "go it alone" on security, amid increased tensions over the future of the transatlantic alliance.

Speaking at the Warsaw School of Economics, Rutte said on Wednesday that the US needed European countries to "step up" on security and that the alliance must become fairer.

"Let me be absolutely clear, this is not the time to go it alone. Not for Europe or North America," Rutte said.

"The global security challenges are too great for any of us to face on our own. When it comes to keeping Europe and North America safe, there is no alternative to NATO," he added.

Rapprochement with Putin

A number of European countries including Germany and Britain have announced plans to hike defence spending as Trump seeks a rapprochement with Russia's President Vladimir Putin in his efforts to end the three-year-old Ukraine war.

Trump has previously said members of the NATO alliance should spend 5% of gross domestic product (GDP) on defence – a significant increase from the current 2% target and a level that no NATO country, including the United States, currently meets.

"Yes, Europe needs to know that Uncle Sam still has our back. But America also needs to know that its NATO allies will step up," Rutte said, adding that the alliance's June summit in The Hague would prove a seminal moment in its history.

"We will begin a new chapter for our transatlantic alliance, where we build a stronger, fairer and more lethal NATO," the former Dutch prime minister said. "A fairer NATO means all allies doing their fair share."