A Seoul court convened a rare hearing on Tuesday into the welfare of a dozen North Korean defectors who South Korea says escaped of their own free will but Pyongyang insists were abducted. The closed-door session pitted officials from South Korea's spy agency, the National Intelligence Service, (NIS) against a group of human rights lawyers who contend the 12 women are being illegally detained. All 12 were waitresses at a North Korean-run restaurant in China who arrived in the South in April, making headlines as the largest group defection in years. While Seoul says they fled to the South voluntarily, Pyongyang claims they were kidnapped by NIS agents and has waged a campaign through its state media for their immediate return. The campaign has included emotional video interviews with the women's relatives in the North, angrily denouncing South Korean authorities and demanding a meeting with the defectors. Seoul has rejected all such advances and insists the women are being held incommunicado for their own protection while they go through a resettlement process. The dispute has fanned inter-Korean tensions that have been running high since the North carried out its fourth nuclear test in January. As the court hearing opened, Japanese and South Korean media cited military and government officials as saying North Korea appeared to be preparing to test a powerful, new medium-range ballistic missile. For all North Korean defectors, life in the South begins with intensive NIS interrogation that can last for months and is aimed at weeding out possible spies. They are then given three months in a government center where they learn basic survival skills, such as riding the subway, using a mobile phone and buying goods in a supermarket. Tuesday's court hearing was ordered at the request of a liberal South Korean legal association called Lawyers for a Democratic Society, which managed to obtain power-of-attorney from the defectors' families in the North. The court had ordered the 12 waitresses to appear in person, but the NIS said they were unwilling to testify because of personal safety concerns and would be represented by legal counsel. As well as challenging the NIS version of events surrounding the defection, the Lawyers for a Democratic Society are pushing the court to allow direct access to the women. But that prospect appeared to dim with the announcement, before the hearing even opened, that the waitresses would be kept under NIS "protection" rather than being sent to the resettlement center like most defectors. The Unification Ministry in Seoul said their case had become too high-profile and the escalating dispute with Pyongyang made them unusually vulnerable. "If we send them to the facility for resettlement training, there will be more media attention and the training will not be conducted smoothly," a ministry official said. "There are bound to be problems," the official said. Nearly 30,000 North Koreans have fled poverty and repression at home to settle in the capitalist South. But group defections are rare, especially by staff who work in the North Korea-themed restaurants overseas and who are handpicked from families considered "loyal" to the regime. The South Korean government estimates that Pyongyang rakes in around $10 million every year from about 130 restaurants it operates — with mostly North Korean staff — in 12 countries, including neighboring China. There have been reports of staff not being paid, with restaurants pressured into increasing their regular remittances to Pyongyang. Earlier this month, South Korea announced that another three waitresses from a different restaurant in China had arrived in Seoul after defecting.