NATO appointed Mark Rutte as its next secretary-general on Wednesday, putting the outgoing Dutch prime minister in charge of the world’s biggest security organization at a critical time for European security as war rages in Ukraine.

Rutte’s appointment was sealed by NATO ambassadors during a meeting at the 32-nation alliance’s headquarters in Brussels. US President Joe Biden and his counterparts will formally welcome him to their table at a summit in Washington on July 9-11.

The outgoing Dutch premier will take over from the current secretary general, Norway’s Jens Stoltenberg, on Oct. 1. Stoltenberg spent more than a decade at the helm. His mandate was repeatedly extended, in part to provide continuity after Russia invaded Ukraine in 2022.