Vice foreign ministerial-level officials of Japan, the United States and South Korea have agreed to prepare together for further possible North Korean provocations, including a nuclear test.

Japan's Vice Foreign Minister Mori Takeo met US Deputy Secretary of State Wendy Sherman and South Korea's First Vice Foreign Minister Cho Hyun-dong at the Iikura Guest House in Tokyo on Wednesday.

The three diplomats agreed that North Korea's test-firings of ballistic missiles in rapid succession are an obvious and grave challenge to the international community.

They also agreed that Russia's claims that Ukraine is preparing to use so-called dirty bombs are false and unacceptable.

On China, they said efforts to unilaterally change the status quo in the East and South China seas by force cannot be condoned, and that they will keep a close eye on the third-term leadership of President Xi Jinping.

Mori later told reporters that cooperation among the three countries has added importance now that the security environment is rapidly growing severe. He pledged to further promote close partnership and cooperation through multilayered communication.

Sherman described Japan and South Korea as strong, close allies. She stressed unwavering US commitment to defending Japan and South Korea, and said the three are bound by shared national security interests.

Cho said the three countries confirmed the need for the strongest-ever response in case the North conducts a seventh nuclear test. He added that they will step up cooperation with the international community so that denuclearization talks can resume.