BRUSSELS -- The NATO alliance this week is getting a new supreme commander, a former top-ranking U.S. military officer in Korea hailed Tuesday by Defence Secretary Ash Carter as a proven warrior-diplomat and "a soldiers' general."

U.S. Army Gen. Curtis M. Scaparrotti was installed as head of the U.S. European Command (EUCOM) in Stuttgart, Germany, and will become NATO's supreme allied commander Europe following a separate ceremony Wednesday at the alliance's military headquarters in southern Belgium.

Scaparrotti, 60, will be the 18th U.S. officer to hold the post since Gen. Dwight D. Eisenhower became the first NATO supreme commander in 1951.

The commander, by tradition an American general or admiral, is responsible for the overall direction and conduct of NATO's global military operations. The 28-nation alliance is now confronted by simultaneous security challenges ranging from a resurgent Russia to armed Islamic extremism and a migrant crisis in the Mediterranean.

"Today our way of life is at a pivotal moment, as we are encountering numerous threats and strategic challenges," Scaparrotti said in brief remarks after assuming command at EUCOM.

Scaparrotti, a West Point graduate and former head of U.S. forces in Korea, had been an "easy pick" as overall American military leader for Europe, Carter said. The defence secretary attended the change-of-command ceremony along with U.S. Joint Chiefs Chairman Marine Corps Gen. Joseph Dunford. While serving in Korea, Scaparrotti proved his ability to work with allies and lead a coalition, Carter said. Fittingly, the Pentagon chief said, there is a bridge named after the general and his father, a World War II veteran, in his hometown of Logan, Ohio.

"General Scaparrotti's success has come from his ability to build bridges between allies and partners, between diverse elements within our joint force," said Carter. He called the four-star general a "soldiers' soldier" who had risen in rank to become a "soldiers' general."

In both new posts, Scaparrotti is assuming command from U.S. Air Force Gen. Philip M. Breedlove, a former F-16 pilot who helped lead the NATO alliance during the most sweeping revamp of its collective defence capabilities since the Cold War.

Carter praised Breedlove's "visionary" leadership, saying that in his three years as SACEUR, "NATO forces have been writing a new playbook" to face modern threats and challenges.

Elizabeth Quintana, director of military sciences at the Royal United Services Institute, said Tuesday she expects Scaparrotti to "be much more forthright" when it comes to dealing with the Russians.

The Obama administration has made it clear that in Europe "it is moving from an assurance posture to a deterrence posture," the London-based expert said.

U.S. forces have shifted primary focus from reassuring NATO partners that they will support them to "overtly stopping or warning Russia that if they try to do anything silly, they will be punished, and that the U.S. and NATO as a consequence will respond," she said.

Russian political and military leaders contend they are doing nothing more than reacting to a menacing NATO military buildup near their borders. Krasnaya Zvezda, the official newspaper of the Russian Defence Ministry, recently called Scaparrotti a "worthy successor" to "self-professed hawk" Breedlove.