SEOUL, South Korea — A nuclear-powered American aircraft carrier arrived Saturday in South Korea for a three-way exercise stepping up their military training to cope with North Korean threats that escalated with its alignment with Russia.

The arrival of the United States Ship Theodore Roosevelt strike group at Busan came a day after South Korea summoned the Russian ambassador to protest a pact reached between President Putin and North Korea’s leader, Kim Jong-un, this week that pledges mutual defense assistance in the event of war.

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 the defense chiefs of America, South Korea, and Japan at Singapore earlier in June, the nations 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 didn’t immediately confirm specific details of the training.

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

The carrier’s visit comes seven months after another American aircraft carrier, the United States Ship 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, America, South Korea and Japan have expanded their combined training and boosted the visibility of strategic American military assets in the region, seeking to intimidate the North.

America 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.