A nuclear-powered United States aircraft carrier has arrived in South Korea ahead of a three-way exercise involving South Korean and Japanese forces.

The countries are stepping up their military training to cope with North Korean threats, which have escalated with its alignment with Russia.

The arrival of the USS Theodore Roosevelt strike group in Busan came a day after South Korea summoned the Russian ambassador to protest over a pact reached between Russian President Vladimir Putin and North Korean leader Kim Jong Un this week that pledges mutual defence assistance in the event of war.

An F-18 fighter aircraft sits in the hangar of the Theodore Roosevelt (CVN 71), a nuclear-powered aircraft carrier, anchored in Busan Naval Base in Busan, South Korea
An F-18 fighter aircraft sits in the hangar of the Theodore Roosevelt (CVN 71), a nuclear-powered aircraft carrier, anchored in Busan Naval Base in South Korea (Song Kyung-Seok/Pool Photo via AP)

South Korea says the deal poses a threat to its security and warned that it could consider sending arms to Ukraine to help fight off the Russian invasion as a response – a move that would surely ruin its relations with Moscow.

Following a meeting between their defence chiefs in Singapore earlier in June, the United States, South Korea and Japan announced Freedom Edge.

The new multidomain exercise is aimed at sharpening the countries’ combined response in various areas of operation, including air, sea and cyberspace.

The Theodore Roosevelt strike group will participate in the exercise that is expected to start within June.

South Korea’s military did not immediately confirm specific details of the training.

South Korea’s navy said in a statement that the arrival of the Theodore Roosevelt demonstrates the strong defence posture of the allies and “stern willingness to respond to advancing North Korean threats”.

Crew members walk by aircraft in the hangar of the Theodore Roosevelt (CVN 71), a nuclear-powered aircraft carrier, anchored in Busan Naval Base in Busan, South Korea
Crew members walk past aircraft in the hangar of the Theodore Roosevelt, anchored in Busan Naval Base in South Korea (Song Kyung-Seok/Pool Photo via AP)

The carrier’s visit comes seven months after another US aircraft carrier, the USS Carl Vinson, came to South Korea in a show of strength against the North.

The Theodore Roosevelt strike group also participated in a three-way exercise with South Korean and Japanese naval forces in April in the disputed East China Sea, where worries about China’s territorial claims are rising.

In the face of growing North Korean threats, the United States, South Korea and Japan have expanded their combined training and boosted the visibility of strategic US military assets in the region, seeking to intimidate the North.

The United States and South Korea have also been updating their nuclear deterrence strategies, with Seoul seeking stronger assurances that Washington would swiftly and decisively use its nuclear capabilities to defend its ally from a North Korean nuclear attack.