Earlier in the day, North Korea launched a ballistic missile, which fell 155 miles off Japan's Okushiri Island, outside the country's exclusive economic zone.
"I believe we, the AP4, should band together with NATO to establish a strong collective security posture. We will have to use this as an opportunity to enhance our cooperation framework with NATO and take a leading role in regional security in the Indo-Pacific region," Yoon said at a meeting with the leaders of Australia, Japan and New Zealand on the sidelines of the NATO summit in Vilnius, as quoted by the South Korean news agency.
Japanese Prime Minister Fumio Kishida reportedly concurred with Yoon's initiative and described the North Korean launch as a threat to international peace and stability, while Australia's Anthony Albanese condemned the launch as violating UN resolutions and affirmed Canberra's solidarity with Seoul.
NATO General Secretary Jens Stoltenberg met with the four Asia-Pacific allies in Vilnius also on Wednesday.
"Good meetings with #NATO's close partners #Australia, #Japan, #NewZealand & #SouthKorea. Security is not regional, it is global — so we are determined to continue," Stoltenberg tweeted after the meeting.
Earlier in the day, Yoon vowed to hold North Korea accountable for its missile launch and convened an emergency session of the National Security Council.
The Wednesday launch was North Korea's first since June 15 and the 12th so far this year. Last year, Pyongyang launched 37 ballistic missiles. The missile reportedly flew a record 74 minutes, with the flight altitude estimated at 6,000 kilometers and the range reaching 1,000 kilometers. The missile was launched at 00:59 GMT and fell outside the exclusive economic zone of Japan at 02:13 GMT, according to reports, citing Japanese and South Korean military.