WASHINGTON — President Donald Trump on Tuesday injected some uncertainty over whether the U.S. would abide by the mutual defense guarantees outlined in the NATO treaty as he headed to its summit — comments that could revive longstanding concern from European allies about his commitment to the military alliance.

“Depends on your definition,” Trump told reporters on Tuesday as he was headed to The Hague, where this year’s summit is being held. “There’s numerous definitions of Article Five, you know that, right? But I’m committed to being their friends.”

Asked later aboard Air Force One to clarify, Trump said he is “committed to saving lives” and “committed to life and safety” but did not expand further.

NATO Secretary-General Mark Rutte said he has no doubt about the U.S. commitment to NATO and its Article 5 guarantee, which says an armed attack on one member is an attack on all. But the remarks from Trump previewed what could be another volatile appearance by him at a summit celebrating an alliance he has often derided.

— The Associated Press