The six-nation talks bring together delegations from North and South Korea, China, Japan, Russia and the US.
Calling for real progress to be made, Hill said the North Koreans needed to work faster to meet international expectations from the talks.
"We should be a little less patient and pick up the pace and work faster"
head of US delegation
"The supply of our patience may have exceeded the international demand for that patience, and we should be a little less patient and pick up the pace and work faster," he said.
The meeting at a secluded Chinese government guest house is the first time the nuclear negotiators have come together since North Korea conducted a nuclear weapons test on October 9.
The test, while condemned by the United Nations, led to renewed efforts to restart the six-party talks, which stalled last year after the North Koreans walked out in protest at US financial sanctions.
According to the South Korean official, who did not give his name, North Korea's list of conditions included demands that the US drop what it called its "hostile policy" towards the communist state.
It also said work must resume on a foreign-funded nuclear reactor for power generation before it would abandon its weapons development programme.
Earlier, Hill, who led the US delegation at the talks, called on the North to "get serious" about ending its nuclear programme.
|North Korea says the US must end|
what it calls its "hostile policy"
"If they get serious with denuclearisation, a lot of good things can happen ... if they do not get serious about denuclearisation such things will go away," Hill said.
At a welcoming banquet for delegates held at the weekend, Hill said he was "neither pessimistic or optimistic" about the outcome of the talks.
North Korea has repeatedly blamed the "hostile policy" of the US, which it says forced it to develop a nuclear weapons programme as a deterrent.
The renewed round of talks is supposed to focus on implementing an agreement reached in September last year, under which North Korea would give up its nuclear programme in exchange for security guarantees and aid.
North Korea, which says it is now a fully fledged nuclear weapons state, is insisting that talks should be seen as negotiations towards arms reduction.
China, which is hosting the talks, said it expected the negotiations to be tough.
"The issues to be discussed and addressed by this meeting are complex and profound, and the tasks borne by all the parties are both glorious and arduous," Wu Dawei, China's deputy foreign minister told delegates at the start of the meeting.