SEOUL (AFP) - South Korea has rejected "absurd and groundless" North Korean accusations that it lured, kidnapped and brainwashed nine young refugees who were repatriated forcibly from Laos to their poverty-stricken communist homeland.

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

The South's unification ministry demanded that North Korea ensure the safety of the refugees, who were arrested in Laos on May 10 and were eventually returned to North Korea via China.

"North Korea was making absurd and groundless allegations, ignoring concerns expressed by our government and the international community over the forced repatriation," the ministry said in a statement late Wednesday.

"The government strongly demand once again that North Korea ensure (their) lives and safety and that they will not receive unfair treatment or punishment."

The North's Red Cross Society earlier on Wednesday insisted 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," it said in a statement.

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.

Seoul has rejected the "trafficker" label saying 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. The North, however, said the returnees were being well-cared for.

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 per cent to 1,508 last year.