The US and North Korea have had "very good" talks aimed at normalising relations between the two nations, the top US negotiator has said.
Mr Hill said he "had very good discussions"
US Assistant Secretary of State Christopher Hill was speaking after the second day of the talks in New York.
He said there was a "sense of optimism" over last month's deal on steps to end North Korea's nuclear programme.
Earlier, a US official said the North must declare all aspects of its nuclear activities for the deal to hold.
"These were very good discussions," Mr Hill told reporters after the second day of the talks with North Korean Vice Foreign Minister Kim Kye-gwan.
"I would say there was a sense of optimism [on] both sides that we will get through this 60-day period and we will achieve all of our objectives that are set out in the 13 February agreement," he said.
Mr Hill was referring to the steps to be taken leading up to a 60-day deadline for Pyongyang to shut down its main plutonium-producing nuclear reactor in return for fuel aid.
The New York talks are aimed at normalising diplomatic relations between the US and North Korea for the first time since they fought each other in the 1950-53 Korean War.
On the agenda is the US designation of North Korea as a terrorist state, as well as the possible lifting of sanctions against it.
Earlier in the day, though, Mr Hill's senior in the state department, Deputy Secretary of State John Negroponte, sounded a warning that North Korea must make a full declaration of all its nuclear activities.
If it omitted any detail "it would have the effect of undermining confidence in this entire arrangement", he said.
Speaking on a visit to South Korea, he said he expected the declaration to describe a uranium enrichment programme.
Doubts were raised last week over US intelligence that asserted the existence of such a programme, and led to the collapse of a previous deal with North Korea in 2002.
A high-level US intelligence officer said that the US only had "mid confidence" that North Korea had used enrichment equipment.
North Korea tested a nuclear bomb last October, but it used plutonium, rather than uranium.
But Mr Negroponte said: "I have no doubt that North Korea has had a highly enriched uranium programme, and that has been and continues to be the judgement of our intelligence community."