In a flurry of diplomatic activity, the gathering in Brunei also saw Beijing pressured over its South China Sea claims while the top US and Russian envoys met to discuss the thorny issues of Syria and US fugitive Edward Snowden.
Participants in the ASEAN Regional Forum, which include 26 countries across the Asia-Pacific and the European Union, sent a "very strong message" to North Korea, Seoul's envoy said.
"Most ministers at the meeting expressed a very strong message to the North Korean delegation that they should denuclearise, they should refrain from provocative action," South Korean Foreign Minister Yun Byung-Se told reporters on the sidelines.
However, North Korean Foreign Minister Pak Ui-Chun fired back in the discussions, calling the United States the "true provocateur" and saying it would retain its nuclear weapons programme until Washington drops its "hostile" stance.
"Unless the US removes all its anti-North policies and threats against us, any problems including the nuclear issues on the (Korean) peninsula will not be solved," North Korean official Choe Myung-Nam told reporters, citing Pak.
A day earlier, US Secretary of State John Kerry said after talks with his counterparts from China, Japan and South Korea in Brunei that the four nations were united on the issue.
A joint statement released hours after the forum ended avoided tough language but "encouraged" Pyongyang to abide by UN resolutions, and called for denuclearisation and peaceful dialogue.
Diplomats also urged a resumption of long-stalled six-country talks hosted by China aimed at negotiating the North's disarmament.
The issue of the South China Sea also simmered on after the Philippines at the weekend accused Beijing of a military build-up to enforce its claims to nearly all of the disputed waterway.
The 10-member Association of Southeast Asian Nations has been pushing a reluctant China for talks on a set of rules governing conduct at sea meant to prevent actions that could lead to conflict.
