The United States said that a North Korean nuclear test would be a "deeply provocative act" and urged the world to let North Korea know such a test would further isolate the already reclusive nation.
State Department spokesman Sean McCormack asked "all the members of the international community, including China, to state very clearly to North Korea that this would be a very provocative act and it would only add to and deepen their isolation".
His comments came amid worry that North Korea might soon test a nuclear bomb. South Korea's main spy agency warned last week that Pyongyang could test a nuclear device at any time.
"This is a matter of concern," South Korea's national security adviser, Song Min-soon, said about the potential for a nuclear test after he met yesterday with Secretary of State Condoleezza Rice. "We will remain watchful on any possibilities."
Song said he and Rice did not speak about the matter during their talks; they discussed broad issues relating to South Korean President Roh Moo-hyun's visit next week to Washington.
McCormack told reporters yesterday that a North Korean nuclear test "would clearly be a deeply provocative act to the international community".
China, seen as North Korea's last major ally, South Korea, the United States, Japan and Russia are working to persuade North Korea to scrap its self-declared nuclear weapons production programme.