South Korea says it deeply regrets failing to stop nine refugees from North Korea being deported back there from China.
Other recent cases have triggered protests in South Korea
The nine were arrested by Chinese police in the city of Shenyang, after they had been placed in a small hotel by South Korea's consulate there.
The refugees said they were relatives of three South Korean prisoners of war.
The same consulate was criticised recently for its treatment of Choi Uk-il, an abductee who fled the North.
Diplomats were accused of initially giving the cold shoulder to the 67-year-old Mr Choi when he arrived in Shenyang, 31 years after he was abducted by the North while out fishing.
Seoul has already apologised over the case of Mr Choi, which caused uproar in South Korea.
South Korea's foreign ministry said the government found it "deeply regrettable" that the nine relatives were unable to come to the country "despite its best efforts".
Choi Uk-il returned to South Korea this week after 31 years
"Taking lessons from this incident, the government will double its efforts to help prisoners of war and their relatives come home safely," it said in a statement.
The nine fled across the North Korean-Chinese border into Shenyang last July, according to the Chosun Ilbo newspaper.
They were placed in a small private hotel by South Korean diplomats in the city, who apparently believed it to be safe.
However, they were arrested in October by Chinese police after a tip-off from the hotel owner and were sent back to North Korea, the newspaper reports.
China does not recognise fleeing North Koreans as refugees, although it has allowed defectors to leave the country if they take refuge at a foreign diplomatic mission.
South Korea believes as many as 485 of its citizens have been kidnapped by the North since the Korean War ended in a ceasefire in 1953.
North Korea insists any South Koreans inside the country defected voluntarily and are not held against their will.
The abductee issue is also a big issue in Japan, where at least 13 people are believed to have been kidnapped by North Korea during the 1970s and 1980s.