NATO says a former U.S. assistant secretary of defense has taken over as the alliance's deputy secretary-general.
Alexander Vershbow replace Claudio Bisogniero of Italy whose term expired this year.
Vershbow, who previously served as a U.S. ambassador to NATO, Russia and South Korea, had coordinated U.S. security and defense policies abroad.
He is the first American to serve in that post. Traditionally, NATO's secretary-general and his deputy are Europeans, while the supreme military commander is a U.S. officer.
Secretary-General Anders Fogh Rasmussen assumed office in 2009.