The United States said Wednesday it would send a rare mission to Myanmar in the coming weeks as it engages the reclusive regime but warned that the diplomacy would be 'slow and painful.' Kurt Campbell, the US assistant secretary of state for East Asia, said the trip would follow up on his talks last month with a senior official in New York -- the highest-level US contact with the military regime in nearly a decade. 'We intend to go to Burma in the next few weeks for a fact-finding mission,' Campbell testified before the House Foreign Affairs Committee, using Myanmar's earlier name. Campbell did not specify who would take part in the trip. Another senior US official, speaking on condition of anonymity, said Campbell hoped to go himself but it would depend on whether the junta gives him access to the opposition. Campbell told the committee that the US mission hoped to meet with the junta as well as detained democracy icon Aung San Suu Kyi and representatives of ethnic groups that have battled the military regime. The junta has kept Aung San Suu Kyi under house arrest for most of the past two decades after her National League for Democracy swept elections in 1990 but was barred from taking power. President Barack Obama's administration has sought to engage US adversaries including Iran, Cuba and Sudan. The administration, in a policy review, last month concluded that the longstanding US approach of isolating Myanmar had failed to bear fruit but said it would not ease sanctions without progress on democracy and human rights. Campbell, who has sought to reassure democracy activists, told the House committee that the dialogue was meant to supplement, not replace, economic sanctions targeting the junta. 'We expect engagement with Burma to be a long, slow, painful and step-by-step process,' Campbell said. 'We will not judge the success of our effort at pragmatic engagement by the results of a handful of meetings. Engagement for its own sake is obviously not a goal for US policy,' he said. Campbell said that one goal was simply to gain a better understanding of the junta, which he described as 'a group of men that have self-isolated themselves.' 'In my particular area, the country that we know the least about at a fundamental level, even less than North Korea, is Burma,' he said. Representative Dana Rohrabacher, a conservative Republican, was sharply critical of the administration's approach. 'With all due respect, we know all about Burma. It's not an unknown quantity. It has a vicious gangster regime, one of the most despicable regimes in this planet,' he said. 'We are saying that they are a legitimate government to sit down with. They are not,' he said. However, many US lawmakers and Myanmar democracy advocates have supported engagement with the regime. Representative Howard Berman, chairman of the Foreign Affairs Committee, said that engagement and sanctions 'must be applied together.' 'Our policy of isolation over the past two decades has resulted in China's growing political and commercial influence in Burma and little progress in supporting those calling for reform,' Berman said. A State Department official, Stephen Blake, quietly visited Myanmar in March to hold talks with both the junta and the opposition. It was the first trip by a senior US envoy to the country in more than seven years. In August, Myanmar's military leader Than Shwe held an unprecedented meeting with a visiting US senator, Jim Webb, a leading advocate of engaging the junta. 