Thailand on Friday urged China and rival claimants to the South China Sea to look beyond border disputes and find ways of cooperating in order to ease tensions in the region.

"Countries in the region should think of sovereignty in less traditional terms in order to support collective security in the long term," Thai Prime Minister Prayut Chan-O-Cha said in a speech opening Asia's largest security forum in Singapore.

"If we look at everything from the standpoint of conflict, we will never be able to see a way out," said the Thai leader, a former army chief who seized power two years ago.

"If we focus solely on borders, some of which are still in dispute, then again, we'll never find a way out," Prayut told the annual meeting known as the Shangri-La Dialogue.

The three-day gathering is being attended by defence ministers and military officials including Pentagon chief Ashton Carter.

Beijing's claim to nearly the entire South China Sea has angered Southeast Asian neighbours and pitted it against the United States, which has conducted patrols near Chinese-held islands to press for freedom of navigation.

The Philippines, Brunei, Malaysia and Vietnam have competing claims in the area, which encompasses key global shipping lanes and is believed to have significant oil and gas deposits.

The Permanent Court of Arbitration in The Hague is expected to issue a ruling soon on a Philippine submission challenging China's claims and activities in the region. Beijing says it will not abide by any ruling.

Ahead of the Singapore conference, US Defence Secretary Carter and his Singapore counterpart Ng Eng Hen flew over the busy Strait of Malacca in a demonstration flight of a US P-8 maritime patrol plane stationed in Singapore, a close military partner of Washington.

"The American approach is an inclusive one in which everyone participates in the collective defence of our peoples from today's threats," Carter said at a joint news conference after the brief flight.

"That's the objective of the US military presence out here, and it's been that way for decades."

- Heated US-China exchanges expected -

Carter did not speak out against China, but has previously condemned Beijing's island building and last week said it risked creating a "Great Wall of self-isolation".

He is scheduled to address the meeting on Saturday, while China's delegation chief Admiral Sun Jianguo will speak on Sunday.

Past editions of the Singapore meeting were marked by heated exchanges between the two sides.

Several US lawmakers were attending the summit as part of a Congressional delegation, including Republican Senator John McCain, who heads the Senate Armed Services Committee.

He said in a lecture before the forum that China must decide if it is going to engage in "coercion and intimidation" or follow a "better path".

"It could cooperate with its neighbours and manage disputes peacefully, consistent with the same international rules that have benefited China so greatly," he said.

Tensions on the Korean peninsula are another concern to be addressed at the forum organised by the London-based International Institute of Strategic Studies (IISS).

The UN Security Council on Wednesday strongly condemned North Korea's latest attempted missile launches and urged world governments to ramp up efforts to impose sanctions on Pyongyang.

Tim Huxley, the IISS Asia head, also said there has been renewed concern over "jihadist terrorism", particularly the threat from organisations and individuals in Southeast Asia who have associated themselves with the Islamic State.

Tensions in the South China Sea are expected to drive up Asia-Pacific defence spending by nearly 25 percent from 2015 to $533 billion in 2020, security think-tank IHS Jane's wrote in a research note issued Thursday.