A Chinese envoy has met North Korea's reclusive leader Kim Jong-il, according to Chinese officials, as tensions mount over the North's nuclear test.
China has warned about expanding UN sanctions against the North
The envoy, former Foreign Minister Tang Jiaxuan, was believed to be carrying a message from China's President Hu Jintao calling for restraint.
The meeting came as a North Korean official hinted at another test.
US Secretary of State Condoleezza Rice has warned of "more grave consequences" if a second test is carried out.
China's Foreign Ministry warned on Thursday against "wilfully" expanding UN sanctions against North Korea.
"Sanctions are a signal, not a goal," spokesman Liu Jianchao told a news conference.
Ms Rice, who is in South Korea on the second leg of an Asian tour to rally opposition to North Korea's nuclear testing, said she hoped China's envoy had sent a "strong message" to Pyongyang.
Her visit follows a UN Security Council vote backing sanctions in response to North Korea's 9 October test.
A North Korean official gave the country's first indication it may be preparing a second nuclear test.
The deputy head of North Korea's foreign ministry, Li Gun, speaking on ABC TV in the US, said a second test would be "natural" and that the US should not be surprised if one were carried out.
President George W Bush said North Korea would face "grave consequences" if it tried to transfer nuclear weapons to third parties such as Iran or al-Qaeda.
Following what she called "fruitful" talks with South Korea's president and foreign minister, Ms Rice said they had discussed ways of preventing the trafficking of nuclear material by North Korea.
South Korea is still considering whether to join the US-led Proliferation Security Initiative (PSI), which was set up in 2003 to inspect ships suspected of carrying materials that could be used for weapons of mass destruction.
NEW UN SANCTIONS
Bans sale to, or export from, N Korea of military hardware
Bans sale or export of nuclear and missile related items
Bans sale of luxury goods
Freezes finances and bans travel of anyone involved in nuclear, missile programmes
Allows inspection of cargo to and from N Korea
Stresses new resolution needed for further action
Ms Rice said reports of US plans for the inspection of cargo involving blockades and quarantines had been exaggerated.
"It is the intention of the resolution to have all states act on their obligation to prevent this trafficking and I think there is much that we can do co-operatively in order to do so," she said.
The South has been reluctant to join PSI for fear of sparking conflict with the North.
Ms Rice began her Asian tour in Japan on Wednesday, meeting Prime Minister Shinzo Abe in Tokyo. She is due to travel on to China.