China and the US discussed warning North Korea against holding a nuclear test, a top American envoy said Wednesday, blaming Pyongyang for holding up six-nation talks on the drawn-out crisis over the isolated regime's nuclear program. US Assistant Secretary of State Christopher Hill's visit to Beijing came amid growing concern 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. That followed reports of suspicious activity at a suspected North Korean underground nuclear testing site. Following a meeting with his Chinese counterpart, Wu Dawei, Hill said the two talked about the need to make very clear to Pyongyang "that this would be a very, very unwelcome development." He did not give any details.