On the eve of a two-day meeting of NATO defense ministers in Brussels, NATO chief Jens Stoltenberg cautioned EU partners not to weaken the alliance with their new armed forces pact.
It wouldn't make any sense for "NATO and the EU to start to compete," adding that there was "no way" the agreement, known as PESCO, could replace the transatlantic alliance in guaranteeing Europe's safety.
Read more: Twenty-five EU states sign PECSO defense pact
The European Union's "permanent structured cooperation on defense agreement" (PESCO) has recently come under fire from US officials who fear it could divert resources away from NATO and undermine the alliance.
Launched in December as a way for EU member states expand collaboration post-Brexit, the framework aims to spend military funds more efficiently.
The United States Ambassador to NATO Kay Bailey Hutchison said that "we do not want this to be a protectionist vehicle for the EU." She said there could be "serious consequences" if the bloc shut US defense companies out of cooperation projects.
Read more: Can PESCO provide a new European identity?
"European allies are absolutely aware that the defense, the protection of Europe is dependent on NATO," Stoltenberg told the defense ministers on Tuesday.
Stoltenberg's warning comes amid pressure on NATO members to step up efforts to increase national defense spending. In 2014 only three members spent more than the target of 2 percent of GDP on defense. Fifteen members have laid out concrete plans to reach these goals by 2024.
kw/kms (AFP, AP)