China, Japan and South Korea said a fresh nuclear test by North Korea would be unacceptable, according to South Korean President Lee Myung-Bak on Sunday.
"Our three countries agreed that we will not accept further nuclear tests or further provocations from North Korea," Lee told reporters after a meeting in Beijing.
Lee met Sunday with Chinese Premier Wen Jiabao and Japanese Prime Minister Yoshihiko Noda for a one-day summit where North Korea's nuclear and rocket programmes had been expected to be high on the agenda.
Fears of a third North Korean nuclear test have grown after a failed rocket launch by Pyongyang last month that the United States and its allies said was a disguised ballistic missile test banned under UN resolutions.
"We should further prevent provocations of North Korea in the future and strengthen cooperation among the three countries in this regard," Noda said.
Wen warned earlier that the region faced many "unstable" factors.
"The various parties need to use their wisdom, keep patient, and display goodwill to the greatest extent so as to ease confrontation and return to the right track of dialogue and negotiations," Wen said.