The United States, Japan and South Korea have agreed to strengthen deterrence to rein in a North Korean "military threat", amid fears that Pyongyang may conduct its seventh nuclear test soon.
Aides to the three countries' foreign ministers said after talks in Tokyo that a North Korean nuclear test would trigger an "unprecedented strong response".
"We agreed to enhance cooperation so that North Korea can stop its irregular activities and return to denuclearization talks," South Korean Assistant Foreign Minister Cho Hyun-dong said after the trilateral meeting.
He stressed that "the three countries agreed on the need for a strong and unprecedented response if North Korea proceeds with its seventh nuclear test."
Japanese Deputy Foreign Minister Takeo Mori said that the three countries will never tolerate what she described as "nuclear blackmail" practiced by Russia in its war against Ukraine.
The diplomats also expressed their countries' opposition to any attempt to change the status quo in the South and East China Seas, in a veiled criticism of Chinese efforts and the military buildup there.
Seoul and Washington have said Pyongyang may be close to testing an atomic bomb for the first time since 2017, following a number of ballistic missile tests that drew widespread international opposition.
One of those missiles flew over Japan last September, and North Korea said it had conducted tactical nuclear tests.
"This behavior is reckless and highly destabilizing," said Wendy Sherman, then US Assistant Secretary of State, urging North Korea to "refrain from further provocations."
North Korean leader Kim Jong Un declared last September that his country's status as a nuclear power was "irreversible", ending negotiations over his country's banned weapons programmes.