North Korea on Wednesday accused the South of having lured, kidnapped and brainwashed nine young North Korean refugees who were recently forcibly repatriated from Laos to Pyongyang via China.

Their case has attracted international concern and condemnation, with the United Nations and human rights groups warning the North that it would be held responsible for the safety of the refugees -- aged between 14 and 18.

But a lengthy statement attributed to a spokesman for the central committee of the North Korean Red Cross Society said the nine were among many people lured away from the country by South Korean government-sponsored human traffickers, posing as religious activists.

"It is an unprecedented and heinous class-A crime -- luring our young children, confining and brainwashing them against their will and trying to drag them to the South," the spokesman said.

The nine refugees were arrested in Laos on May 10 for illegal entry and were eventually returned to North Korea via China.

The Lao foreign ministry said two South Koreans accompanying the refugees were detained for alleged human trafficking and later handed over to the South's embassy in Vientiane.

The foreign ministry in Seoul rejected the "trafficker" label and said the two were acting as "guides" and trying to secure the refugees' permanent escape from the North.

Most North Korean refugees begin their journey by crossing into China, where they face repatriation if caught.

They then try to make it to a third country -- Thailand is the most popular choice -- from where they generally seek permission to resettle in South Korea.

Those who are caught and deported back to the North face severe punishment including a jail term at a labour camp, defectors in Seoul and rights groups say.

But Wednesday's statement carried by the North's official Korean Central News Agency said the nine "kidnapped" returnees were being well-cared for.

"These young children who were luckily brought back to their beloved homeland... are stabilising and will flourish under the care of the nation to fulfil their hopes and future," the spokesman said.

Condemning what it described as the "farce" of South Korea warning the North over the fate of the refugees, the spokesman said they had been "beaten with iron-clubs" by the South Koreans who lured them away.

"If the enemy sticks to its anti-North schemes, including attempts to kidnap our nationals despite our warnings, it will pay a steep price," he said.

The UN High Commissioner for Human Rights and the US State Department have both criticised Laos and China for being complicit in the return of the young refugees to North Korea.

Since the end of the Korean War in 1953, some 25,000 North Koreans have escaped and settled in the South.

But North Korean leader Kim Jong-Un is believed to have tightened border controls since he came to power after the death of his father Kim Jong-Il in December 2011.

The number of refugees arriving in South Korea plunged more than 40 percent to 1,508 last year. (AFP)