Some 50 letters sent by South Korean prisoners of war who still remain in North Korea provide a revealing insight into their plight. The letters, obtained by the Chosun Ilbo, were sent by the survivors to relatives in the South between 2000 to 2005.

They were carried by couriers from North Korea to South Korean activists in China and then passed on. Many were sent from North Hamgyong Province on the northern edge of the reclusive country.

Some letters did not reach the families members in South Korea or were rejected by the recipients. "They were often rejected when immediate family members had died and distant relatives received the letter," said one South Korean activist in China.

All of the letters are on coarse paper, hinting at the squalid living conditions of the POWs. Some describe the food shortage in North Korea and plead for financial help, but most of the POWs simply wanted to hear how their family members and friends are doing or asked for a chance to hear their voices over the phone.

Many end with a terse comment saying that they are unable to go into details, presumably because they worried about getting caught.

The Defense Ministry estimates that around 500 South Korean POWs are still alive in North Korea.

Between the end of the 1950-53 Korean War and the 1960s, the UN Command held 11 meetings with the North Korean military to demand the return of South Korean POWs. At the time, the UN and the government here estimated that around 24,000 South Korean were still being held there. Only 8,343 POWs were returned to the South when the Korean War ended in an armistice.

North Korea claimed that all South Korean POWs had been returned and none remained in the North, but the government here confirmed through interviews with North Korean defectors and South Korean POWs who returned that many more remained.

But it has come under consistent fire for not doing enough to get them home.

In defense ministers' talks between North and South Korea in 2000, the South urged the North to resolve the issue. But North Korea refused. South Korea again raised the issue during the inter-Korean ministerial talks in 2006 and defense ministers' talks in 2007, but again there was no response from the North.

Instead, the government here included POWs in a list of people separated from their families by the war that it sent to North Korea ahead of family reunions and was able to confirm that 19 were still alive and 14 had died. Seventeen of the surviving POWs were briefly reunited with relatives in South Korea.

Since efforts to free them failed, South Korean POWs have been escaping North Korea by any means possible. From 1994 to 2010, 80 fled and returned to the South. But none has made it out since 2011.

"Not only has North Korea bolstered security checks along its border with China, but South Korean POWs are finding it more difficult to cross the border on their own as they grow older," a Defense Ministry official here said.

