Top diplomats from Japan, the United States and South Korea have agreed to continue working together on steps to counter North Korea, which has deepened military cooperation with Russia.

A Japanese foreign ministry official later said that their meeting in Tokyo on Monday was proof that there is no problem with their cooperation on the matter, despite the recent political turmoil in South Korea.

The Japanese Foreign Ministry's Asian and Oceanian Affairs Bureau Director-General Namazu Hiroyuki discussed North Korea with US Assistant Secretary of State for East Asian and Pacific Affairs Daniel Kritenbrink, and Cho Koo-rae, South Korean Vice Foreign Minister for Strategy and Intelligence.

They discussed a Russia-North Korea strategic treaty that has come into force, which includes a mutual pledge to provide military assistance if either comes under attack. They reiterated their serious concerns over Russia and North Korea's growing military cooperation, including the deployment of North Korean troops to Russia.

The diplomats reconfirmed the importance of close coordination among their three countries. They also agreed to continue working together towards the full implementation of relevant UN Security Council resolutions and on steps to counter North Korea's illicit cyber activities. They said such cyber operations help Pyongyang finance its program to develop weapons of mass destruction.

The gathering comes after South Korean President Yoon Suk-yeol declared martial law, which he quickly reversed.