Amid unconfirmed reports North Korea is preparing for an underground nuclear test in a northeastern region, Chinese Premier Wen Jiabao, Japanese Prime Minister Yoshihiko Noda and South Korean President Lee Myung-Bak issued the warning after a meeting in Beijing, Russia's RIA Novosti news agency said.
"Our three countries have agreed that we will not accept further nuclear tests or further provocations from North Korea," the South Korean leader said.
In Seoul, an unidentified military source told the Yonhap news agency any nuclear testing would contravene a 1992 non-nuclear treaty.
Satellite intelligence images suggest North Korea has an underground test site under development with extensive tunneling, the reports said.
A month ago, Pyongyang defied international warnings and test-fired a ballistic missile, which exploded and crashed seconds after launch.