A nuclear-powered U.S. aircraft carrier, the Theodore Roosevelt, arrived in the South Korean port city of Busan on Saturday to take part in joint military exercises later this month with the host nation and Japan, naval officials said.

The leaders of the three countries agreed at a summit last August to hold annual military training drills as they sought to project unity in the face of China's growing power and nuclear threats from North Korea.

This month's drills, called "Freedom Edge," will involve the three countries' navies and include maritime, anti-submarine warfare exercises and air defense exercises, said U.S. Rear Admiral Christopher Alexander, commander of the Carrier Strike Group Nine.

"The intent is to improve the interoperability between our navies and ensure that we are ready to respond to any crisis or contingency," he told a press conference, saying the Theodore Roosevelt would serve as the command ship for the drills.

Last year, the three counties also staged joint naval missile defense and anti-submarine exercises to improve responses to North Korean threats.

Russian President Vladimir Putin visited North Korea this week for the first time in 24 years and signed a deal with leader Kim Jong Un that included a mutual defense pledge.

It was one of Russia's most significant moves in Asia for years, which Kim described as amounting to an alliance.

The visit comes seven months after a South Korea trip by another U.S. aircraft carrier, the Carl Vinson, in a show of extended deterrence against the North's nuclear and missile programs.