The United States and North Korea wrapped up historic talks on establishing diplomatic ties on an optimistic note Tuesday but the US wants Pyongyang to "come clean" about any uranium enrichment program and eliminate all nuclear weapons before normalizing relations. "These were very good, very businesslike, very comprehensive discussions," US Assistant Secretary of State Christopher Hill told reporters at the end of two days of meetings that lasted more than eight hours. "For now, I think we feel we're on the right track." His North Korean counterpart, Vice Foreign Minister Kim Kye Gwan, was also upbeat, telling reporters "the atmosphere was very good, constructive and serious." Under a Feb. 13 agreement reached at six-nation talks in Beijing, North Korea must shut down its main nuclear reactor and allow UN inspectors back into the country within 60 days. In return, the North would receive aid equal to 50,000 tons of heavy fuel oil from the other countries in the six-party talks on its nuclear program - the United States, South Korea, Russia, China and Japan. Hill said "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." The Feb. 13 timetable is the first step toward implementing a September 2005 agreement in which North Korea agreed to abandon its nuclear programs in exchange for energy aid and security guarantees. Hill said he was encouraged by Kim's willingness to look ahead to the more difficult next stage, which calls for the country's plutonium-producing reactor to be disabled and then dismantled - and for North Korea to make a full disclosure of its entire nuclear program. Experts estimate North Korea's reactor at Yongbyon, north of the capital, has produced about 110 pounds of plutonium, that "we have reason to believe has been weaponized," Hill said. US Deputy Secretary of State John Negroponte said Washington also has "no doubt" that North Korea has a uranium enrichment program, an allegation that brought on the nuclear crisis with the North in 2002. Pyongyang has never publicly acknowledged having such a program. Hill said North Korea spent a lot of money buying centrifuges, manuals, aluminum tubes and other equipment for what appears to be a Pakistani-designed program to enrich uranium, and "they need to come clean on it" and ultimately abandon it. During a lengthy discussion with Kim on the highly enriched uranium issue, Hill said, they agreed to resolve the matter before North Korea makes its final nuclear declaration to the six nations and the International Atomic Energy Agency. US and North Korean experts will meet in order "to get to the bottom of this matter," he said. Hill told a news conference he "made the point forcefully today" that North Korea cannot denuclearize if highly enriched uranium - which can be used to produce nuclear weapons - "is still out there." The primary focus of the first meeting of the US-North Korea Working Group, one of five established under the Feb. 13 agreement, was steps toward establishing diplomatic relations. Hill said Washington looks forward not only to eventual normalization of relations but to creating peace on the Korean peninsula and ensuring security in northeast Asia. The United States has never had diplomatic relations with North Korea, which was created after World War II when Korea was split into a communist-dominated North and a US-backed capitalist South. North Korea and South Korea remain technically at war because the armistice at the end of the 1950-53 Korean War has never been replaced by a peace treaty. In Tuesday's talks on normalizing relations, Hill said one issue that was discussed was North Korea's desire to get off the US list of state sponsors of terrorism. He said he raised legal, political and historic issues, "some of them stemming from incidents in the 1980s and before." Another issue that was raised was North Korea's desire to get off the list of countries subject to the US Trading with the Enemy Act, which would open the way for a normal trading relationship with the US for the first time. Hill said he also discussed with Kim the legal and political steps involved in normalization. Hill said he doesn't think North Korea likes the idea of establishing liaison offices as an interim measure, which was "a very successful model" used ahead of restoring US-China ties. "I think they would like to move to diplomatic relations, but I must say this is very much linked to denuclearization," Hill said. He would not predict when the last piece of nuclear material will be taken out of North Korea, but said: "We believe that the faster we go the steadier we'll be." "Let us do this step-by-step - get through 60 days and take the next thing, which I think is measured in months, and not years, and then go on from there," he said. On March 19, Hill said the six parties will meet in Beijing to make sure that all the required 30-day actions were met. Under the Feb. 13 agreement, the five working groups must meet within 30 days. Hill said the US Treasury will meet the 30-day deadline to ease financial restrictions against North Korea. Just before March 19 meeting, Hill said the US-North Korea Working Group will meet again, and the working groups on nuclear issues, energy and economic assistance, and northeast Asia security will meet for the first time, all in Beijing. Envoys from Japan and North Korea met in Vietnam on Tuesday, ahead of two-day talks of their working group starting Wednesday aimed at establishing diplomatic relations. Japan's chief envoy Koichi Haraguchi said Japan wants to spend ample time discussing North Korea's history of abducting of Japanese citizens. North Korea wants Japan to atone for the 1910-45 colonization of the Korean Peninsula and wartime atrocities, including sex slavery of tens of thousands of Korean women. Hill said he had a long discussion with Kim about the Japanese abductions and made "a strong pitch" that it was "very important" for North Korea "to reach out and develop relations with Japan." "I was pleased to see there was a positive understanding," he said. In April, foreign ministers of the six parties will meet in Beijing in April to review the first 60 days, "to discuss the upcoming phase, but also to look more broadly and more far reachingly out toward the future to address the problem of ... replacing the armistice with a peace mechanism and ... creating a Northeast Asia security mechanism," Hill said. In a related issue, South Korea's Yonhap news agency reported Tuesday that a senior aide to South Korea's president will visit North Korea this week and speculated his goal was to set up a summit with North Korean leader Kim Jong Il. But officials in Seoul denied a summit was in the works.