The top U.S. envoy dealing with North Korea has conferred with Chinese officials on warning Pyongyang against testing a nuclear weapon.

Christopher Hill speaks to the press

Assistant Secretary of State Christopher Hill said he and Chinese diplomats discussed the need to make very clear to North Korea that testing a nuclear device would be - a "very, very unwelcome development."

"They [the Chinese], like us, are concerned about this," he said. "We did not get into any discussion of what may or may not be clear signals on the ground, but we certainly discussed the danger that the D.P.R.K. could try to take additional provocative steps."

Hill met Wednesday with Wu Dawei, China's top negotiator in six-nation talks aimed at ending North Korea's nuclear weapons programs.

Hill's trip to Asia, which also includes stops in Japan and South Korea, comes as intelligence officials warn that North Korea may be preparing for an underground nuclear test.

Hill on Wednesday called on China to start implementing U.N. Security Council resolution 1695, which condemns North Korea for its missile tests two months ago. The U.S. envoy says the Chinese continue to favor a diplomatic solution without the use of sanctions.

"China remains very focused on how to get the diplomacy working again," he said. " But I made very clear to the Chinese that we are proceeding to look for all ways pursuant to the requirements of 1695 to be vigilant and that we would expect the Chinese to do the same pursuant to their obligations. We did not get into specifics of how that vigilance would be implemented."

The resolution, approved unanimously by Security Council members - including China - calls for U.N. members to prevent the transfer of money, technology and other tools that North Korea could use to make weapons of mass destruction.

Although China is expressing growing frustration with North Korea for failing to return to multi-party talks on nuclear disarmament, Beijing is reluctant to resort to sanctions against its neighbor.

Analysts say this is because Beijing fears sanctions would destabilize North Korea, sending a wave of refugees into Chinese territory, and causing the collapse of one of China's last remaining communist allies in the region.