North Korea came under fire at an Asia-Pacific security forum Tuesday as foreign ministers called on the defiant communist state to end its nuclear weapons programme.

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.

"So they have to listen to these messages very seriously."

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.

China is the main ally of North Korea, which defiantly carried out its third nuclear weapons test in February and threatened to attack the United States, in language shrill even by the standards of the reclusive communist state.

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.

Philippine Foreign Secretary Albert Del Rosario told reporters that one foreign minister after another at Tuesday's event stressed the need for negotiations on avoiding conflict at sea.

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.

China claims virtually all of the South China Sea and has long resisted moves to talk with ASEAN as a bloc, reluctant to cede any ground on its claims.

On Sunday in Brunei it agreed to begin discussing a code of conduct.

But a senior US government official, speaking on condition of anonymity, dismissed the move as merely a gambit to deflate pressure while in Brunei.

On the final day of a series of related diplomatic events in the sultanate, Kerry said he and his Russian counterpart, Sergei Lavrov agreed on the need to hold an elusive international conference to end Syria's civil war.

Russia has backed Syrian President Bashar al-Assad in the more than two-year conflict that has claimed more than 100,000 lives, while Washington has said it is boosting support for the rebel movement.

Kerry said "we both agree that the conference should happen sooner rather than later".

However, despite some hopes that the conference could be held this month, Kerry said it was unlikely until after August.

Their meeting took place under a cloud spawned by the sensational case of Snowden, who has been in limbo for a week in a Moscow airport in a bizarre, globe-circling asylum bid.

Snowden had worked as a contractor for the US National Security Agency before his leaks on a global US surveillance programme began emerging in early June, roiling Washington's relations with China, Russia and Europe.

Kerry said he raised the sensitive issue with Lavrov but the exchange failed to yield any progress on an impasse that has further strained testy US-Russian ties.