The United States should not reward North Korea's "bad behavior" toward rival South Korea, top US military officer Mike Mullen said Sunday, adding that Pyongyang is striving to "get attention."

In an interview with CNN, Mullen, the chairman of the US joint chiefs on staff, said North Korean leader Kim Jong-Il's "unpredictability" made it difficult to understand the regime's motivations.

"I am one who believes we shouldn't be rewarding bad behavior here. And yet he continues to generate that behavior in hopes that he can get attention -- enough attention to move in some direction that's, quite frankly, not determined," Mullen said.

His comments came as the United States and South Korea began naval operations in a potent show of force, just days after Pyongyang bombarded a South Korean island, killing four people.

"I believe his main focus is to continue to develop nuclear weapons, to continue to get the world's attention and to continue to try to move himself up to a level that is regarded as a, you know, sort of a world player," Mullen said of Kim.

Mullen also called on China to take a stronger stand against Pyongyang, which he said poses a serious threat.

"It's hard to know why China doesn't push harder," he said, adding they try to keep Kim under control.

"I'm not sure he is controllable," Mullen said.

The risk, "if we get it wrong, all of us, including China," is that North Korea could, eventually, "be able to threaten ballistically -- a ballistic missile capability which will threaten the United States and others."

Earlier Sunday, China called for "emergency consultations" in Beijing early next month among chief envoys to the stalled six-nation talks on the North's nuclear disarmament.

Its top envoy on North Korea, Wu Dawei, speaking in Beijing, stressed the proposal did not constitute a formal resumption of the negotiations. But he said he hoped they would lead to such a resumption soon.

China has not joined other world powers in criticising the North's island bombing.

The war games, involving at least 11 ships and spearheaded by the massive US nuclear-powered aircraft carrier the George Washington, aim to send a message of deterrence to the North.

The exercises are part of a series announced in May, after a Seoul-led multinational investigation found overwhelming evidence that a North Korean torpedo had sunk a South Korean warship in March, killing 46.