BRUSSELS — One of NATO’s longest serving top officials, Secretary-General Jens Stoltenberg, stepped down on Tuesday, handing over the reins to former Dutch Prime Minister Mark Rutte as the military alliance confronts some of the biggest challenges in its history.

The new leader of NATO, former Netherlands Prime Minister Mark Rutte, pledged on Tuesday to continue leading the alliance in its support of Ukraine and called out China as an "enabler" of Russia in its invasion.

NATO's new chief Mark Rutte voiced strong support for Ukraine on Tuesday and said he was not worried about the upcoming U.S. election as he could work with former President Donald Trump or Vice President Kamala Harris.