President Yoon Suk Yeol boarded a visiting US nuclear-powered aircraft carrier on Tuesday ahead of joint drills between South Korea, the United States and Japan aimed at enhancing their responses against rising threats from North Korea.

Yoon visited the USS Theodore Roosevelt (CVN-71), which made a port call at a naval port in the southeastern city of Busan. The carrier is set to participate in a trilateral naval drill, dubbed Freedom Edge, the first-ever trilateral multidomain exercise, which kicks off on Wednesday.

Yoon said the aircraft carrier’s visit is part of “extended deterrence” measures outlined in the Washington Declaration adopted at his summit with US President Joe Biden in April last year, reports Yonhap news agency.

Extended deterrence refers to Washington’s commitment to using the full range of its military capabilities, including nuclear weapons, to defend its ally.

“It symbolises the firm US security commitment to South Korea, including strong extended deterrence,” Yoon was quoted as saying.

The aircraft carrier’s visit came amid rising concerns over evolving threats posed by North Korea after it signed a comprehensive strategic cooperation treaty with Russia, which includes a pledge for the two countries to come to each other’s aid if attacked.

Yoon stressed the importance of enhancing trilateral security cooperation with the US and Japan.

“The cooperation between South Korea, the US, and Japan, which share the values of liberal democracy, will become another powerful deterrent alongside the South Korea-US alliance,” he said.

This marks the third time an incumbent South Korean president has boarded a US aircraft carrier, following former President Park Chung-hee in 1974 and President Kim Young-sam in 1994, according to the presidential office.

The USS Theodore Roosevelt made a port call for the first time in South Korea. It also marked the first arrival of a US aircraft carrier here in seven months.

Earlier in the day, Yoon condemned the deepening military and economic cooperation between Pyongyang and Moscow as “anachronistic” acts that go against the progress in history and blatantly violate UN Security Council resolutions.

On Monday, North Korea slammed the arrival of the USS Theodore Roosevelt in South Korea and warned of taking “overwhelming and fresh” deterrence measures against what it called a “provocative act.”

Pyongyang has long denounced joint military drills between Washington and Seoul and also the US dispatch of its strategic assets to the Korean Peninsula as a rehearsal for an invasion of the North.