"The European Union cannot defend Europe. Eighty percent of NATO's defence expenditures come from non-EU NATO allies," Stoltenberg, secretary general of the North Atlantic Treaty Organization, told Reuters in an interview.
Stoltenberg said it was clear that Europe's security depended not just on Europe itself but on other NATO members such as the United States, Canada, Turkey, Norway and Iceland.
"If you just look at the map, it's obvious that all these countries, non-EU allies, are vital for the protection of Europe," he said.
He added that "any attempt to de-link Europe from North America will also divide Europe". Many European nations, particularly in Eastern Europe, see the U.S. as their primary security guarantor and would oppose any move to change that.
Trump, the U.S. ex-president and frontrunner to be the Republican nominee in this year's presidential election, sparked sharp criticism from Western leaders after saying he had told NATO members the U.S. would not defend those who failed to spend enough on defence and would even encourage Russia to attack them.
Many European politicians said Trump's comments were a wake-up call and should act as a spur for Europe to do more to be able to defend itself.
Stoltenberg said European NATO members had to do more to build up defence capabilities and were doing so. But he said this should happen within a transatlantic framework.
Earlier on Wednesday, he said European allies would invest $380 billion in defence this year, taking their spending to an estimated 2% of total GDP in 2024, compared to 1.85% in 2023.
(Reporting by Andrew Gray and Johnny Cotton; editing by Charlotte Van Campenhout and Mark Heinrich)
By Andrew Gray and Johnny Cotton
