YOKOSUKA - The US Navy is increasingly worried about tensions on the Korean Peninsula after Pyongyang tested a nuclear device, a move that could spur closer military ties between neighbors South Korea and Japan, a senior US officer said on Friday.
"A huge explosion occurred, and that should make all countries concerned," Vice Admiral Joseph Aucoin, commander of the US Seventh Fleet, told reporters aboard the aircraft carrier the USS Ronald Reagan south of Tokyo.
He said the Seventh Fleet stood ready to support US forces in South Korea if necessary.
Previously tense relations between Japan and South Korea have improved recently, notably with a landmark agreement seeking to end tensions over Korean women and girls forced to work in wartime Japanese military brothels.
The US government and weapons experts have voiced doubts about whether the device tested by North Korea on Wednesday was a hydrogen bomb, as Pyongyang had claimed.