"I'm pretty convinced the Chinese would have a very strong message about future tests," said the State Department official accompanying US Secretary of State Condoleezza Rice, who arrived on Thursday in South Korea.
The official, speaking on condition of anonymity, described the delegation led by State Councillor Tang Jiaxuan as very high-powered, including all of Beijing's key officials on North Korea.
The State Department Wednesday confirmed Tang's visit. "My understanding is that his trip would be part of Chinese efforts to convince the North Koreans to comply with (UN) Resolution 1718, as well as the other relevant Security Council measures that are out there," added a State Department spokesman, Tom Casey.
China, the North's only major ally, has not confirmed the visit.
Tang last week met US President George W. Bush in Washington and also visited Moscow.
The UN resolution, unanimously approved on Saturday by the Security Council, calls on North Korea to return to negotiations about its nuclear program and imposes sanctions on the impoverished state for its October 9 nuclear test.
In Pyongyang, Li Gun, the deputy head of North Korea's foreign ministry, hinted a second test was on the way.
"That is natural, so we don't have to care much about this issue," he told US television network ABC. Asked if the United States should not be surprised by a second test, Li replied: "That's right, yes."
Rice is on the second leg of a four-nation tour of Asia and Russia to urge the North's neighbours to strictly enforce the sanctions.

Copyright AFP (Agence France-Presse), 2006