"I know everyone's concerned about the date, but the real issue is to make sure we get something that's complete," he said.
Hill was speaking ahead of talks with Song Min-soon, South Korea's foreign minister, to discuss efforts to push ahead with the North's nuclear disarmament.
He had already met officials in Tokyo and plans to head to Beijing and Moscow next as he discusses strategy with the other members of the six-party talks process.
But Hill said there were no plans to visit North Korea or meet North Korean officials on this trip.
Last week the North missed a key year-end deadline to disable its nuclear facilities and provide a full declaration accounting for all its nuclear programmes in return for aid and political concessions.
It said it gave a list of its nuclear programmes to the US in November and tried its best to meet its obligations.
Asked about that list, Hill said: "They can make as many declarations as they want. The issue is, have they made a complete one, and the answer is no."
The US wants North Korea to address its suspected uranium enrichment programme, a sticking point that sparked the current nuclear standoff in late 2002, but the North denies ever having such a programme.
|Protesters in Seoul held an anti-North|
Korea rally as Hill arrived[AFP]
Hill said the North had "not wanted to list certain programmes that we know about and they know that we know about".
But he added Washington had held "considerably detailed discussions" with the North, leaving it in no doubt about what the US wants in the declaration.
"I think they understand what we are looking for in a complete declaration, so I don't think there's any misunderstanding there."
He added that the US was not looking to use the North's declaration to cause further problems to the process, "but what we can't do is to pretend that there are not programmes when we know there are programmes".
Despite the delay in the declaration, disablement work – primarily focused on the reactor at Yongbyon - was still progressing, Hill said.
"Disablement … really has gone well. I know there's talk about it slowing down, but frankly, a lot of actions have been completed. I think everybody involved in the process has been very satisfied with the pace of disablement."
He said what delays there were had occurred as a result of safety and technical issues.