HANOI:  Asia-Pacific`s biggest security dialogue opened in Vietnam on Friday with the United States and South Korea seeking a statement condemning North Korea over the sinking of a South Korean warship in March.

US Secretary of State Hillary Clinton is expected to ask China to do more to rein in its communist ally during bilateral talks with Foreign Minister Yang Jiechi in Hanoi, amid escalating tensions on the Korean peninsula.

The two are expected to meet on the sidelines of the 27-member ASEAN Regional Forum (ARF), which is also being attended by North Korean Foreign Minister Pak Ui-Chun.

The other three countries involved in stalled six-party talks on North Korea`s nuclear programme -- Japan, Russia and South Korea -- also will be represented but officials expect little progress on resuming the dialogue.

Clinton set the tone when she announced fresh sanctions against the North during a trip to South Korea on Wednesday.

The United States and South Korea are also planning a massive naval drill -- involving a US aircraft carrier, destroyers and thousands of troops -- from Sunday in the Sea of Japan as a deterrence against North Korean "aggression".

Pyongyang denies sinking the warship and has warned of war if it is punished, citing a UN Security Council statement on July 9 which condemned the incident but did not identify a culprit.

The North says it has been vindicated by the statement, which was watered down under pressure from its ally China.

Seoul and Washington are understood to be hoping for stronger wording from the ARF, citing an international probe which found evidence that a North Korean submarine had fired a torpedo at the ship in the Yellow Sea.

China, meanwhile, has warned against the US-South Korean military exercises, with a spokesman calling on "all sides to maintain a cool head and exercise restraint".

The drills were moved from the Yellow Sea to the Sea of Japan in response to Chinese objections. A North Korean spokesman on Thursday condemned the exercises as a threat to global peace.

State Department spokesman Philip Crowley repeated Washington`s line that the exercises were defensive, and said the North was the real provocateur.

"Actions by North Korea, including the sinking of the Cheonan ... those kinds of provocative steps do in fact pose a threat to security and stability in the region," Crowley said in Washington.

Diplomats said South Korea is engaged in intense lobbying to wring a strong statement of condemnation of North Korea from the ARF, whose core is the 10-country Association of Southeast Asian Nations (ASEAN).

A draft ARF declaration expresses "deep concern" over the Cheonan incident and "supports" the UN Security Council statement.

Unlike the UN statement, however, it does not acknowledge the results of the South Korean-led international probe or the North`s denials, skipping the question of responsibility altogether.

The draft ARF declaration also calls for the resumption of the six-party talks -- an idea already floated by Pyongyang but rejected by Seoul and Washington unless the North demonstrates sincerity.

South Korean Foreign Minister Yu Myung-Hwan said there was no chance of resumption until Pyongyang demonstrated its sincerity and stopped provocative actions.

"North Korea must show genuine willingness and make progress in denuclearisation before the six-party talks can take place," he said in Hanoi on Wednesday.

Friction over the sinking of the Cheonan has further tested already strained relations between Washington and Beijing, which froze military ties with the United States in January over arms sales to Taiwan.

BDST: 0922 HRS, July 23, 2010