BANDAR SERI BEGAWAN – China's territorial disputes with its neighbours and choking smog in Southeast Asia are among the contentious issues set to dominate a major regional forum kicking off this weekend.

The annual diplomatic and security meetings hosted by the Association of Southeast Asian Nations will this year be held in Brunei against a backdrop of escalating tensions over increasingly assertive Chinese maritime territorial claims.

The foreign minister-level talks, which climax Tuesday with the ASEAN Regional Forum that includes China, the United States, Russia and other heavyweights, are further spiced by the Sino-US spat over fugitive intelligence leaker Edward Snowden.

Snowden's revelations of US government monitoring of phone and Internet traffic have drawn Chinese criticism, stoking mutual distrust already heightened by the Obama administration's strategic "pivot" to Asia.

The US has accused China of letting Snowden slip out of Hong Kong, an allegation Beijing disputes. Snowden is now at Moscow's airport and is said to be seeking asylum in Ecuador.

Russia has angered the United States by refusing to extradite Snowden and the Brunei event is an opportunity for US Secretary of State John Kerry to discuss the issue with his Russian counterpart, Sergei Lavrov.

The meetings begin with a gathering of the 10-member ASEAN bloc on Sunday, expanding Monday to include China, Japan and South Korea, before an East Asia summit gathering 26 countries and the European Union.

Last year's meetings were marred by sharp disunity within ASEAN over how to confront Beijing's growing assertiveness in staking its claim to virtually all of the East Sea.

ASEAN has sounded a more unified tone of late, and will press China in Brunei for "urgent" talks on a "code of conduct" meant to ease tensions, Indonesian Foreign Minister Marty Natalegawa said.

"We need to stop this pattern of testing the will of each other. It is extremely dangerous and full of potential for a miscalculation," he told AFP.

Competing claims have for decades made the sea a potential flashpoint. Animosity has re-emerged in recent years with several confrontations involving China, mainly with Vietnam and the Philippines.

In a move likely to anger China, which insists the United States has no role to play in the East Sea, Kerry is expected to raise the issue in Brunei.

"We would expect ministers at the ASEAN Regional Forum to discuss competing territorial claims to the [East Sea] and to reinforce regional principles, including mutual respect, self restraint, and peaceful resolution of disputes in accordance with international law," a State Department spokesman told AFP.

"We encourage all parties to manage these disagreements peacefully and to make rapid meaningful progress on a code of conduct."

China has long resisted ASEAN efforts to create a legally binding code to govern conduct on the sea, and regional security expert Ian Storey said Beijing would continue to oppose anything weakening its claims.

"A code of conduct is going to take several years to negotiate. In the meantime, tensions will remain as they are now or probably go up," Storey, from the Institute of Southeast Asian Studies in Singapore, told AFP.

China and Japan also are at loggerheads over competing claims in the East China Sea, and that dispute could also be raised in Brunei.

Such gatherings are closely watched each year for bilateral meetings on the sidelines.

In addition to Lavrov, Kerry will meet with his Chinese counterpart, Wang Yi.

Seoul has said a meeting between the foreign ministers of South and North Korea could also be on the cards.

After a series of threats against Seoul and Washington that renewed concerns about its nuclear programme, North Korea has backed off, offering direct talks with the United States and sending two envoys to its ally Beijing recently.

Meanwhile, the talks will be held as Indonesia struggles to contain slash-and-burn farming in its giant rainforests that has in recent weeks sent toxic smoke across to smother Malaysia and Singapore.

Those two countries are under public pressure to push Indonesia at the Brunei gathering for more aggressive and systematic action to curb the land clearing.

"We need to put in place a permanent solution to prevent this problem from recurring annually," Singapore Prime Minister Lee Hsien Loong said this week after Indonesian President Susilo Bambang Yudhoyono apologised for the crisis to Singapore and Malaysia.