SEOUL (AFP) - The United States and South Korea told North Korea on Saturday to show it is serious about scrapping its nuclear weapons programme, amid moves to restart long-stalled six-party disarmament talks. US Secretary of State Hillary Clinton and the South 's Foreign Minister Kim Sung-Hwan also called for a "resolute" international response to the North 's uranium enrichment programme - a potential second route to an atomic weapon. Clinton was paying a brief visit to the close ally, where the US bases 28,500 troops, and will meet Sunday with South Korean President Lee Myung-Bak before flying to earthquake-hit Japan. She and Kim called on the North to "demonstrate its genuine determination in denuclearisation with actions," according to a South Korean foreign ministry statement after their talks. They agreed that the uranium programme disclosed last November violates UN resolutions and a 2005 six-nation denuclearisation deal, and said "the international community should respond resolutely". They also said that inter-Korean dialogue on denuclearisation should be a priority in resuming the six-party talks - a position resisted in the past by Pyongyang, which insists it should talk to Washington. A senior US official said the United States was firm on South Korea 's role, believing it was crucial to ease tensions after last year's North Korean shelling of a civilian island and the sinking of the South 's Cheonan warship. North Korea often says it "would be prepared to take some small steps, many of which could then be subsequently reversed," the official said after the talks. "We're not interested in replaying that loop. What we're looking for is a fundamental change in the way North Korea interacts with its neighbours, particularly South Korea ," he said. Clinton's visit to Seoul comes amid a renewal of diplomatic activity over North Korea . Former US president Jimmy Carter, an advocate of reaching out to Pyongyang, is expected to visit later this month with fellow elder statesmen. US President Barack Obama took office with a goal of reaching out even to US adversaries. But he has taken a hard line on North Korea , which carried out nuclear and missile tests in 2009, just months into the new US administration. Away from the North Korea question and hoping to address a key concern for the Lee administration, Clinton gave assurances that the United States was committed to ratification of a free-trade deal. "I'm very encouraged and determined about the passage of the free trade agreement," she said at the meeting with Kim. "I'm very confident that there will be a positive outcome that will benefit both of our countries." The agreement, which will remove 95 percent of tariffs between the two economies, has been controversial in both countries, with the main US union confederation saying that big businesses would be the main beneficiary. But Obama's administration last year won over many holdouts within his camp when South Korea agreed to revisions, including slowing down the elimination of US tariffs on car imports. Despite the public hard line on North Korea , the United States may be obliged to pursue diplomacy once again to free a US citizen arrested after crossing into the tightly controlled country. The United States has in the past sent former presidents, including Carter and Bill Clinton, to win the release of Americans held in North Korea while insisting that such efforts were a one-off and not part of a broader outreach. In Japan, Clinton will meet Prime Minister Naoto Kan and have tea with Emperor Akihito and Empress Michiko, an unusual Sunday function for the Imperial Palace. The United States, which stations 47,000 troops in Japan, launched a round-the-clock military effort dubbed "Operation Tomodachi," or "friend," to ferry supplies to the tsunami-devastated northeastern coast. The disaster has temporarily cast aside disputes between Japan and the United States, including over the location of a Marine base that has been unpopular with some residents of the southern island of Okinawa.