China will play the key role in curbing North Korean aggression despite US efforts to change Pyongyang's behaviour with sanctions and a show of military strength, analysts said Thursday.

In a strong demonstration of solidarity with their South Korean ally over the sinking of a warship, top US officials in a visit this week announced new sanctions and a major naval exercise designed to deter the North.

South Korea and the United States, citing the results of a multinational investigation, accuse the North of torpedoing the Cheonan corvette in March with the loss of 46 lives.

Pyongyang angrily denies any involvement.

US Secretary of State Hillary Clinton said Wednesday the sanctions aimed to pressure Pyongyang and stop the regime bankrolling its atomic programme or spreading nuclear arms.

And Defense Secretary Robert Gates said there were some signs of possible further provocations following the Cheonan attack, "as the succession process gets under way in the North".

Ailing leader Kim Jong-Il, 68, is widely reported to be preparing to name his youngest son as eventual successor.

Some analysts said the joint South Korea-US war games starting Sunday -- involving 20 ships, 200 planes and 8,000 military personnel -- could be a deterrent.

But most saw China's role as more important -- to ensure the effectiveness of the new sanctions against its wayward ally and to deter provocations.

The North's existing economic woes would also discourage adventurism.

Washington acknowledged the role of Beijing, which keeps Pyongyang's foundering economy afloat.

"We will be consulting with China (on) what we think (are) additional steps that it can take," said State Department spokesman Philip Crowley.

Korea University professor Yoo Ho-Yeol said he expects no further serious attacks on the South for a while.

"North Korea is now in a dire situation economically," he told AFP. "So it may not want a further escalation of tensions around the peninsula and will be under pressure from China."

Pyongyang has had years of practice outsmarting US and UN sanctions.

"In order for the new sanctions to work powerfully, the United States must cooperate with China, which will be unlikely to support the US action," said Yang Moo-Jin of Seoul's University of North Korean Studies.

Large-scale military drills would also not deter provocations, Yang said, but the chances of attacks on South Korea were slim.

"North Korea has enough problems at home. And it would be difficult for it to push ahead with military provocations without approval from China, which would hardly agree with such acts of raising tension."

Kim Yong-Hyun of Seoul's Dongguk University said new sanctions could cause the North stress. But neither these nor the war games would be likely to change its behaviour.

Attacks on the South were, however, unlikely since the North was "looking for an exit strategy" from the Cheonan incident.

Not all analysts accept the North's guilt. Those who do believe North Korea torpedoed the Cheonan say the succession issue may have provided a motive.

The military could also have wanted revenge for the damage it suffered in last November's inter-Korean naval clash, said Daniel Pinkston, Northeast Asia deputy project director for the International Crisis Group think-tank.

"The sinking also sends an internal signal of ruthlessness on the leadership's part," he told AFP. "If it is willing to risk war, it would have no problem using deadly violence against anyone plotting a coup or resisting the succession plans."

China's cooperation in implementing the new sanctions would be "absolutely crucial," Pinkston said.

The war games would remind the North's military "of the kind of force the US can project and that they cannot win any full-scale military conflict."

While the drills could boost Pyongyang's hardliners, the US and South Korea must respond to the sinking, Pinkston said.

"It doesn't get much more serious than sinking a naval vessel. If you don't respond to that with a show of force, when will you?"