NATO Secretary General Mark Rutte said at a forum in the U.S. state of Iowa that the wording of Article 5 of the alliance’s founding treaty is deliberately ambiguous.

According to Rutte, the goal is to prevent potential adversaries from knowing in advance when NATO might activate its collective defense mechanism. He added that in the event of hybrid attacks, alliance members have a broad range of possible responses.

Rutte said not all of those measures would necessarily be made public and that NATO’s reaction could be either symmetrical or asymmetrical, depending on the circumstances.

He also acknowledged that European members of the alliance had long relied heavily on the United States, expecting Washington to carry much of the burden. According to Rutte, that approach is now changing as global threats increase and NATO places greater emphasis on strengthening its own resilience.

Article 5 states that an armed attack on one NATO member is considered an attack on the alliance as a whole and requires allies to provide assistance.

In 2024, NATO broadened its understanding of the scenarios that could trigger Article 5, adding cyberattacks as one possible basis for invoking the collective defense mechanism.