North Korea must do more if stalled six-party talks on ending its nuclear drive are to resume, a US envoy said Thursday as he wrapped up an Asia tour aimed at gauging if Pyongyang is ready to negotiate.

Stephen Bosworth, Washington's point man on North Korea, was in Beijing on Wednesday and Thursday for talks with Chinese Foreign Minister Yang Jiechi and Beijing's special Korea envoy Wu Dawei on how to revive the negotiations.

"We are convinced of the need to resume diplomatic activities and we will also continue the exchanges of views in the coming weeks and months," Bosworth told reporters.

"It is clear that the six-party process does not just depend on the five. It also depends on what we hear and see from the DPRK," he said, referring to North Korea by its official acronym.

"The burden is quite clearly on the DPRK."

The six-party talks involving North and South Korea, China, Japan, Russia and the United States had previously secured North Korean pledges to give up its nuclear programmes, but Pyongyang stormed out in April last year.

China, which hosts the talks, on Thursday called for more contact between the countries involved.

"The two sides (China and the US) believe that relevant parties should increase dialogue and contact and create conditions for the early resumption of the six-party talks," foreign ministry spokeswoman Jiang Yu told reporters.

Bosworth visited Seoul and Tokyo this week before his final stop in Beijing. He was headed back to Washington from China, a US embassy spokesman told AFP.

His counterparts from China, Japan and South Korea each recently visited Washington for talks.

The March sinking of a South Korean naval vessel that left 46 sailors dead has remained a key obstacle to restarting the denuclearisation talks, with South Korea and the United States blaming the incident on North Korea.

Pyongyang has adamantly denied involvement.

Bosworth said Thursday there was "no indication" that the North was in any way ready to apologise for the incident.

He underscored the importance of Sino-US cooperation on the issue, and said Washington was pleased with the briefings it had received from the Chinese side on North Korean leader Kim Jong-Il's visit last month to China.

During that visit, Kim reportedly told Chinese President Hu Jintao that he was willing to return to the six-party talks, without offering any firm time commitment.

US President Barack Obama's administration has insisted on what it calls "strategic patience," saying it will not rush into talks and instead wants North Korea to make clear it abides by a 2005 deal to give up nuclear weapons.

US officials and analysts expect the United States will eventually sit down for formal talks with North Korea. But few foresee a breakthrough amid signs the nuclear-armed regime is in the throes of leadership succession.

North Korea has apparently delayed its most important political gathering in 30 years -- a meeting to elect the "highest leading body" of the Workers' Party of Korea, amid speculation the ailing Kim could anoint his son to succeed him.

Senior North Korean officials have told international agencies in Pyongyang that the delay was due to storm damage, Seoul's Yonhap news agency quoted a source as saying.

Former US president Jimmy Carter called on the United States to pursue peace "aggressively" with North Korea, saying its leaders told him they wanted better relations with the world.

In his first public remarks on his mission last month to the reclusive communist state to free a US prisoner, Carter said that North Korean leaders voiced concern over recent pressure by South Korea and the United States.

"Still, they said, they were ready to demonstrate their desire for peace and denuclearisation," Carter wrote in an op-ed piece Thursday in The New York Times.

"They referred to the six-party talks as being 'sentenced to death but not yet executed,'" Carter said.