Six-nation talks on North Korea's nuclear program should wait for the outcome of an investigation into the unexplained sinking of a South Korean warship, the chief US negotiator indicated Thursday.

In line with a statement by South Korea, the US special envoy on North Korea, Stephen Bosworth, said the United States was in a "posture of waiting" to learn why the Cheonan warship sank in March, killing 46 people.

"Our focus is on supporting the ROK as it tries to establish exactly what happened with the Cheonan," Bosworth said when asked about talks, referring to South Korea by its official name, the Republic of Korea.

South Korean President Lee Myung-Bak has hinted that North Korea was involved in the sinking of the Cheonan and promised a "resolute" response when the cause is established following the multinational probe.

"I think it would be premature to speculate about where we're likely to be in the longer term other than to say that I think we remain committed to, obviously, diplomacy and dialogue," Bosworth said on Thursday.

"We also expect that North Korea will demonstrate a similar commitment to diplomacy and dialogue in an effort to make serious progress on the issues that divide us," he said at a forum of the East-West Center.

North Korea's leader Kim Jong-Il was said to express readiness to return to the long-stalled six-nation disarmament talks in discussions Wednesday with China's President Hu Jintao, according to South Korea's Yonhap news agency.

North Korea, which has tested two nuclear bombs, last year bolted from the six-nation talks under which it had agreed to give up its nuclear program in return for badly needed aid and security guarantees.

The isolated communist state eventually said it would return to talks after pressure from China, its main ally. But the North later said it wanted to negotiate a permanent peace treaty with Washington before nuclear dialogue.

"We have refused to accept any preconditions and believe strongly that the formula for North Korea relieving itself of the sanctions imposed under Security Council Resolution 1874 ... is in the resolution itself," Bosworth said.

He was referring to the Security Council resolution imposed last year after North Korea's second nuclear test which demanded that Pyongyang to take irreversible steps to end its nuclear program.

The resolution called on all nations to inspect North Korean cargo to prevent its exports of missiles and other military hardware, a key money-earner for the impoverished regime.

State Department spokesman Philip Crowley voiced hope that China made a "strong statement" to North Korea that the regime "comply with international law."

"It needs to comply with international law. It needs to cease its belligerent behavior and take action to improve relations with its neighbors," Crowley told reporters.

"Let's see North Korea take these steps and then we'll talk."