Washington's top delegate to the North Korea nuclear talks has returned to Asia to discuss the North's unfulfilled nuclear promises. Pyongyang missed an end-of-year deadline to list all its nuclear activities, but it says it already upheld its part of the bargain, and is issuing new rhetorical attacks on the United States. VOA's Kurt Achin reports from Seoul.

U.S. Assistant Secretary of State Christopher Hill called for "patience and perseverance" with Pyongyang as he arrived in Tokyo Monday. He has a week of shuttle diplomacy ahead of him, as he tries to nudge the North back on the road to nuclear disarmament.

Pyongyang promised last year to detail all of its nuclear facilities and programs by the end of the year, as a prelude to dismantling them. Its detailed list, however, has yet to appear.

On Friday, the North Korean Foreign Ministry said it had sufficiently declared its programs to the U.S. in November. A ministry spokesman was quoted as saying the North "has done virtually all it can" under last year's agreement.

South Korean Foreign Ministry spokesman Cho Hee-young says Seoul regrets the North's failure to produce the declaration. He says what Pyongyang provided in November is not sufficient.

He says North Korea did indeed discuss some elements of its declaration with U.S. envoy Hill, but provided none of the formal documents it promised.

The U.S. says China - the nation chairing the six-nation talks on the North's nuclear programs - has received no declaration from Pyongyang.

The major sticking point appears to be what Washington says is a secret uranium-enrichment program started by the North. Pyongyang has denied having such a program, and Hill indicates that no such program has been included in the North's preliminary listing of its nuclear activities.

In recent days, North Korea has revived a vow to boost what it calls its nuclear "deterrent," and has accused Washington of trying to dominate other countries.

Pyongyang also says South Korea and the U.S. are late delivering the energy aid that they promised as their part of last year's nuclear deal. Seoul and Washington dispute this.

Brian Myers is an international relations professor at South Korea's Dongseo University. He says the rhetoric, and Pyongyang's failure to declare its weapons, are North Korean leader Kim Jong Il's way of keeping the tension high.

"We need to remember that tension with the United States is absolutely essential to Kim Jong Il's political survival," said Brian Myers. "His regime derives its entire legitimacy from the claim that it is protecting North Korea from the American threat. So for him, I think, the six-party talks are a way for him to keep the tension within manageable limits."

Hill is scheduled stop in South Korea, China and Russia later this week.

While here in the Seoul, he is due to meet with president-elect Lee Myung-bak, who says he will take a harder line against Pyongyang than the incumbent president, Roh Moo-hyun.