Washington's top North Korea negotiator said Wednesday that the key to breaking a deadlock over a disputed inventory of the North's nuclear programs is still missing. US Assistant Secretary of State Christopher Hill met in Beijing with his Chinese counterpart, Wu Dawei, along with top negotiators from South Korea and Japan. China is the host of international talks on North Korea's nuclear program grouping those five nations and Russia. "I want to stress that we haven't yet arranged for all the factors, all the elements that we need to be put together," Hill told a news conference. "We have a lot of work ahead of us. I don't want to suggest we've had any major breakthroughs," he said.