SEOUL (Reuters) - North Korea accused South Korean activists on Wednesday of trying to kidnap nine young people who the United Nations and South Korea believe were forced back to their homeland by China last week.

The United Nations said last week it was concerned about China's return of the nine to North Korea, where they face severe punishment, possibly execution, for having fled. The nine were first sent back to China after crossing into Laos.

Hundreds of North Koreans attempt to flee from their country every year, often first crossing into China and then making their way to Southeast Asia. Many end up at a reception center in Bangkok from where they are flown to South Korea.

The South Korean Foreign Ministry said the nine had been "forcibly deported to the North" after they were picked up by North Korean agents in Laos as they tried to make their way to South Korea.

But the North's KCNA news agency said South Korean "elements" had tried to trick the nine and take them to the South.

"Recently, a case of an unprecedented anti-humanitarian act of atrocity has been disclosed where traitorous puppet elements tried to trick and kidnap our youths and drag them to South Korea," the KCNA news agency said.

North Korea refers to the South as a U.S. puppet.

Some experts in South Korea say the North might try to use the nine in a propaganda campaign against the South or against international rights groups.

KCNA, quoting a spokesman for the North's Red Cross central committee, said the nine were forced to read Christian literature and had been given information critical of North Korean in an attempt to bring them to the South.

The South Korean government should "punish the instigators and apologize for the criminal act", KCNA said.

The South Korean government has come under criticism at home for failing to stop the deportation of the nine from Laos to China and back to North Korea.

Media said North Korea sent special agents affiliated with its secret police to escort the nine to China and North Korea.

Chinese Foreign Ministry spokesman Hong Lei said the nine returned to the North last week but denied North Korea has sought to have them returned.

More than 20,000 North Korean defectors have made their way to South Korea, many via Southeast Asia, and many with the help of South Korean human rights groups, religious organizations or commercial brokers.

(Reporting by Jack Kim; Editing by Robert Birsel)