BRUSSELS - U.S. President Joe Biden said on Monday that NATO is "critically important" for American interests and, speaking just before the start of a summit of the defence alliance in Brussels, added that he wanted Europe to know the United States was by its side.

"Article 5 is a sacred obligation," he said, referring to the transatlantic alliance's collective defence doctrine. "I want all Europe to know that the United States is there."

(Reporting by Marine Strauss and John Chalmers) ((john.chalmers@tr.com; +32 470 88 14 91;))