North Korea's failure to meet a deadline to declare its nuclear activities needs to be confronted with patience and perseverance, a senior U.S. envoy said on Monday.

North Korea said on Friday it had already accounted for its nuclear arms programme as required under a multilateral disarmament deal, but the assertion was quickly rejected by the United States, which pressed Pyongyang for a declaration.

"They were prepared to give a declaration which wasn't going to be complete and correct and we felt that it was better for them to give us a complete one even if it's going to be a late one," Washington's top envoy to nuclear talks with North Korea, Christopher Hill, told reporters.

"We understand that this is always a difficult process, one that is rarely completed on time. So I think we have to have a little sense of patience and perseverance," he added, after arriving in Tokyo for talks with his Japanese counterpart.

The United States and several allies have said that North Korea missed a December 31 deadline to submit a full inventory of its nuclear arms programmes, as promised in six-party nuclear negotiations last year.

At the talks -- which group the two Koreas, the United States, China, Japan and Russia -- Pyongyang agreed to abandon its nuclear programme in exchange for aid and better international standing.

A spokesman for South Korea's Foreign Ministry said Pyongyang had not handed the list to China, which chairs the six-party talks.

"As far as we know, there was a consultation between North Korea and the United States about the nuclear declaration but we have not heard of North Korea submitting the list," said spokesman Cho Hee-young.

Hill said he was prepared to move forward in the nuclear negotiations but not without a "complete and correct declaration" from Pyongyang.

North Korea has made progress in disabling facilities at its Yongbyon complex, including a Soviet-era reactor, a plant that produces nuclear fuel, and another that turns spent fuel into plutonium.

"Of course no one likes being late, but being late is probably preferable than being wrong or giving us something that we can't work with," said Hill, who will travel to Seoul, Beijing and Moscow after Tokyo.