US Secretary of War Pete Hegseth has said Europe must take the lead on building out a revamped "NATO 3.0" and creating a "real, hardline military alliance".

Hegseth made the comments while speaking ahead of a meeting with his NATO counterparts in Brussels on Thursday.

"NATO 3.0 is post-Cold War recognition that needs to go back to a real, hardline military alliance that has real military capabilities capable of deterring right here on the continent and taking the lead for the conventional defence of Europe," Hegseth said.

US president Donald Trump has repeatedly pushed for European NATO allies to divert more money to defence spending and has signalled his intention to scale back the United States' role in the alliance, as he turns his attention more to China and the Indo-Pacific region.

In May, Washington reportedly told NATO members it would reduce the number of bombers, fighter jets, warships and other military assets destined for the alliance.