A U.S. aircraft carrier arrived in the South Korean port city of Busan on Friday for the first time in nearly five years to join naval exercises in a show of strength amid concern North Korea may conduct what would be its seventh nuclear test and first since September 2017.

The arrival of Ronald Reagan, with nearly 5,000 crew on board, and warships from its accompanying strike group comes after North Korea adopted legislation detailing its policy on the use of nuclear weapons earlier this month.

Stressing the "watertight" relationship that the United States and South Korea have had as allies in the past 70 years, Rear Adm. Michael Donnelly, commander of the carrier strike group, said that the carrier's operation around the Korean Peninsula symbolizes Washington's vow to deal with any threat in the region.

Nuclear-powered U.S. aircraft carrier USS Ronald Reagan arrives in the South Korean port city of Busan on Sept. 23, 2022. (Kyodo)

"The Republic of Korea and the United States have one of the most successful alliances in the world," Donnelly said at a press conference. "We have a history of shared blood. We share common values and have a clear vision for a free and open Indo-Pacific."

The nuclear-powered Nimitz-class aircraft carrier, commissioned in 2003, is the only U.S. forward-deployed aircraft carrier.

The carrier, based in the Japanese city of Yokosuka, south of Tokyo, last entered the South Korean port in October 2017, when the situation surrounding the peninsula was tense following missile and nuclear tests by North Korea.