One possibility is that they may have crossed into North Korea illegally from China, the BBC’s Lucy Williamson in Seoul says. Unofficial travel to North Korea by private citizens from South Korea is illegal,Pyongyang’s state news agency announced the detention of several unnamed South Korean nationals in 2010 and there is speculation that they may be among those returned, our correspondent adds.

The move by North Korea is seen as a gesture of reconciliation following the cancellation of reunions for families split by the division of the Korean peninsula at the end of the Korean War which were planned for last month. Tensions between the two Koreas rose earlier this year, after North Korea’s third nuclear test in February.

Source: www.bbc.co.uk