WASHINGTON (Yonhap) -- The United States on Wednesday expressed skepticism about North Korea's proposal for unconditional dialogue with South Korea to ease tensions, saying Pyongyang must first apologize for recent provocations and show commitment for denuclearization.

 "We all understand that ultimately to resolve the challenge of North Korea, there has to be dialogue," State Department spokesman Philip Crowley said. "We're open to dialogue, but it's not just for North Korea to say, 'OK, fine, we'll come talk.' There has to be an appropriate context."

 North Korea recently made a series of conciliatory gestures since tensions rose to the highest level since the end of the 1950-53 Korean War last year with the shelling a South Korean front-line island and sinking of a South Korean warship.

North Korea in November revealed a uranium enrichment plant that observers fear could serve as a second way of producing nuclear bombs, aside from plutonium. Pyongyang claims it is producing fuel for power generation.

Pyongyang earlier in the day called for unconditional dialogue with South Korea.   

South Korea instantly rebuffed the proposal as insincere because it came with no apology for the artillery attack on Yeonpyeong Island and the torpedo attack on the Cheonan.

Crowley buttressed Seoul's stance.

"Within the last few weeks, you've seen a shelling of South Korean territory, which resulted in the loss of both civilian and military lives," he said. "North Korea has yet to take any responsibility for that unprovoked act. North Korea to this day has not accepted any responsibility for the sinking of the Cheonan."

U.S. Secretary of State Hillary Clinton earlier in the day met with Chinese Foreign Minister Yang Jiechi, and reaffirmed the need for the North to meet its obligations under a six-party deal signed in 2005 for its denuclearization in exchange for economic aid and diplomatic benefits, Crowley said.

"Both sides affirm that we want to see North Korea meet its obligations under the 2005 joint statement," the spokesman said. 

"We reaffirm that we're open to dialogue, but there are definitely things that North Korea has to do to signal that there is a true seriousness in purpose before we commit to these negotiations. We stressed that there has to be the appropriate context to be able to move forward either with bilateral dialogue or with multilateral dialogue."

Yang is here to discuss preparations for Chinese President Hu Jintao's visit to Washington this month.   

"We had a discussion today about how the upcoming visit and discussion between the president and President Hu Jintao, together with our respective teams, can chart the best way forward to ease tensions on the peninsula, get North Korea to be a more constructive player in the region and take those kinds of steps that would convince all of us that dialogue will be useful," Crowley said.

Clinton and Yang discussed North Korea "in the greatest detail," the spokesman said.

In a separate news briefing, White House spokesman Robert Gibbs said that North Korea will be high on the agenda at the upcoming summit between Obama and Hu on Jan. 19. 

"I would say that understand that human rights, the global economy and currency are certainly on the list," Gibbs said. "Of course the situation in North Korea I anticipate will also take up some amount of that time."

China, the host of the six-party talks, has called for their early resumption without preconditions as a way to ease tensions on the Korean Peninsula.

Jack Pritchard, president of the Korea Economic Institute, and Abraham Kim, vice president of the KEI, said in an article on the institute's Web site that Obama's meeting with Hu will serve as "a good barometer for what is to come."

"North Korea will be a main summit agenda item and the Obama administration will call for responsible pressure by Beijing on Pyongyang to end its provocative behavior and return back to denuclearization in a serious manner," they said. "Whether the U.S. will be able to persuade China to take this harder stance will be a key development to watch in 2011."

Stephen Bosworth, U.S. special representative for North Korea policy, is currently on a tour of South Korea, China and Japan to discuss ways to revive the nuclear talks, stalled since December 2008 over North Korea's missile and nuclear tests, and other provocations.

Upon arriving in Seoul Tuesday, Bosworth said he wants to restart negotiations with North Korea "at a reasonably early date."

He met with South Korean Foreign Minister Kim Sung-hwan and other officials and left for Beijing earlier in the day without meeting with the press for an unknown reason.

The flurry of diplomacy comes amid hopes for rapprochement in inter-Korean ties as both Koreas are reaching out to one another to ease tensions.

South Korean President Lee Myung-bak said Monday that the door for inter-Korean dialogue is still open.

Lee also said last week he wants to achieve the North's denuclearization through the six-party talks and inter-Korean dialogue this year, ahead of the North's plans to become a "strong and prosperous state" by 2012, the 100th anniversary of the birth of the North's founder, Kim Il-sung, father of current leader Kim Jong-il.

North Korea has put forth a series of conciliatory gestures through New Mexico Gov. Bill Richardson, who visited Pyongyang last month, including its intentions to reinstate inspectors from the International Atomic Energy Agency at its Yongbyon nuclear facilities.

The monitors' reinstatement is among the preconditions Seoul and Washington have set before the reopening of the multilateral nuclear talks, involving the two Koreas, the U.S., China, Japan and Russia.

North Korea expelled IAEA monitors in early 2009 in the wake of U.N. Security Council sanctions for a missile test. Months later, Pyongyang detonated its second nuclear device, after the first detonation in 2006, drawing harsher U.N. sanctions.