China and South Korea have again called on North Korea to return to stalled nuclear talks, saying they will renew effort to restart the negotiations. Concerns are mounting that the North might be planning a nuclear test soon.

The Chinese state-run news agency Xinhua quoted Chinese President Hu Jintao and South Korean President Roh Moo-hyun as saying all sides in the talks should continue work to resolve the North Korean nuclear crisis through peaceful dialogue.

The two leaders were in Moscow for commemorations marking the end of World War II in Europe. The South Korean leader said his country expects China to take an active role in getting Pyongyang to rejoin negotiations.

As North Korea's chief supplier of food and fuel, Beijing is seen as having the most influence over the reclusive communist state. But Chinese officials have consistently said their ability to sway North Korea is limited.

Stephen Noerper is an expert on North Asia security issues at the Nautilus Institute, a California organization that studies global problem solving. Speaking in Beijing, he said that while China has called for a nuclear-free Korean peninsula, it perhaps lacks sufficient incentive to push Pyongyang harder. He says Beijing dreads a collapse of the North's government, led by Kim Jong Il.

"I think China is willing to accept a nuclear North Korea, as long as it has stability," said Mr. Noerper. "For North Korea, it is all about regime stability. For China, it is just about stability in northeast Asia."

Many regional political analysts say Beijing fears that a collapse of the government could lead to instability in the North and push hundreds of thousands of refugees into China from its impoverished neighbor.

Concern has risen after recent reports out of Washington that North Korea might be preparing for a nuclear test. Pyongyang says it has manufactured nuclear weapons and will make more. The head of the International Atomic Energy Agency says North Korea may have five or six bombs.

Six-nation talks on the nuclear issue, involving the Koreas, China, Japan, Russia, and the United States, have been stalled since last June. At that session, the United States proposed offering Pyongyang security guarantees and other benefits if it gave up its nuclear programs in a verifiable manner.

North Korea never responded to the proposal and has given various reasons for not returning to the negotiations. Among other things, it has said the United States must first drop what Pyongyang says is a hostile attitude toward North Korea.

The North in the past also demanded bilateral negotiations with the United States, a condition Washington dismisses. On Sunday, North Korean officials appeared to reverse that position, with the state news agency saying Pyongyang has never requested talks independent of the six-party negotiations.

The United States has urged North Korea to return to negotiations without conditions, saying the six-party talks remain the best option that North Korea has to resolve the nuclear issue peacefully.