The three nations agreed at talks in Washington on Friday to hold regular missile defence and anti-submarine exercises in their efforts to boost diplomatic and military cooperation.

North Korea tested a new solid-fuel intercontinental ballistic missile (ICBM) on Friday that experts say would ease the way for missile launches with little warning, part of an increase in its military activities in recent weeks.

Hours after the trilateral exercises, Ri Pyong Chol, vice president of the North Korean ruling party’s Central Military Commission, issued a statement criticising the U.S. for calling a U.N. Security Council meeting over its ICBM test.

The North’s weapons development was a self-defensive measure of defence against the U.S., Ri said. He accused Washington of raising regional tensions “to the brink of explosion” with military drills simulating a “pre-emptive nuclear strike and an all-out war” against the North.

The recent deployment of U.S. strategic bombers was “clear evidence that the U.S. nuclear threat and blackmail against us has reached a level that cannot be overlooked”, Ri said.

“If the U.S. ignores our repeated warnings and continues actions that endanger the security environment of the Korean peninsula, we will take necessary action so that it feels a clearer security crisis and insurmountable threat,” he added.

Monday’s drills in international waters between Korea and Japan bring together South Korea’s 7,600-tonne Aegis destroyer Yulgok Yi I, the U.S. guided-missile destroyer Benfold, and Japan’s Atago destroyer, also equipped with Aegis radar systems.

The effort focuses on mastering response procedures, from detection and tracking to information-sharing, by creating a virtual target in a scenario featuring a North Korean ballistic missile provocation, the South’s navy said.

“It is an opportunity to strengthen trilateral security cooperation against North Korea’s escalating nuclear and missile threats,” Captain Kim Ki-young of the South Korean destroyer said in a statement.

This would solidify the navy’s capability and posture to respond to ballistic missiles, he added.

Japan’s defence ministry said the exercises promote trilateral cooperation on regional security challenges, and demonstrate the three countries’ strong commitment to secure a free and open international order based on the rule of law.

Pyongyang has threatened “more practical and offensive” action as South Korean and U.S. forces have performed annual springtime exercises since March, some involving Japan, which the North has described as a rehearsal for nuclear war.

Separately, the air forces of South Korea and the United States are set to begin drills on Monday for a 12-day run.

Also on Monday, South Korea and Japan resumed “two-plus-two” talks of senior diplomatic and security officials in Seoul after a five-year halt, as their ties thaw after a years-long feud over issues of wartime history.

They share views on North Korea and regional issues, while agreeing to improve understanding of each other’s policies and foster security cooperation in a “forward-looking” way, Seoul’s foreign and defence ministries said in a joint statement after the meeting.

President Yoon Suk Yeol, who has pledged to move ties with Japan beyond the past, visited Tokyo in March for the first time in 12 years as South Korea’s leader.

By Hyonhee Shin

(Reporting by Hyonhee Shin; Additional reporting by Elaine Lies in Tokyo; Editing by Lincoln Feast, Clarence Fernandez, Philippa Fletcher and Mark Heinrich)