US Defense Secretary Lloyd Austin, who is in Seoul for annual security talks, met with his South Korean counterpart Shin Won-sik while Japanese Defence Minister Minoru Kihara joined the meeting online.

"The three ministers assessed ... that preparations for the operation of real-time missile warning data sharing mechanism is in the final stages and agreed to officially activate the mechanism in December," Seoul's defence ministry said in a statement.

The top officials also agreed to put in place a multi-year plan for regular trilateral drills by the end of 2023 for more "systematic and effective" training starting January, it added.

During the meeting, "the three leaders assessed regional security issues, including the growing nuclear and missile threats from the Democratic People's Republic of Korea (DPRK)," the US Department of Defense said in its statement.

The ministers were following up on agreements reached by their leaders at a three-way summit hosted by US President Joe Biden at Camp David in August.

Seoul and Washington have ramped up defence cooperation in the face of a record-breaking series of weapons tests by Pyongyang this year.

South Korea's conservative government of President Yoon Suk Yeol has also made a concerted effort to improve historically strained ties with Japan, the country's former colonial ruler.

The Camp David meeting marked the first time the three leaders had met for a standalone summit, rather than on the sidelines of a larger event.

The defence chiefs also condemned growing military cooperation between North Korea and Russia as a violation of UN resolutions, according to the statement from Seoul's defence ministry.

Historic allies Russia and North Korea are both under international sanctions -- Moscow for its invasion of Ukraine and Pyongyang over its nuclear weapons and missile programmes.

Their growing military cooperation has been a source of concern for Ukraine and its allies, especially following North Korean leader Kim Jong Un's summit with Russian President Vladimir Putin in September.

Sunday's meeting came just days after US Secretary of State Antony Blinken visited Seoul and warned military ties between Pyongyang and Moscow were "growing and dangerous".