The US, Japan and South Korea vowed on Wednesday to deepen cooperation in the face of repeated "provocations" from North Korea, calling its actions a threat to stability in the region and beyond.
Washington and its allies believe North Korea could be about to resume nuclear bomb testing for the first time since 2017, after it launched an unprecedented number of ballistic missiles this year.
"South Korea, the US and Japan agreed that an unparalleled scale of response would be needed in case North Korea conducts a seventh nuclear test," a South Korean official told a joint news conference in Tokyo.
First Vice Foreign Minister Cho Hyun-dong was speaking after a meeting with his US and Japanese counterparts.