A senior North Korean official said on Wednesday that the announcement was equivalent to a "declaration for confrontation" that could jeopardize the diplomatic process, AFP reports.
South Korea deported two North Koreans back to the communist nation after learning that they killed 16 fellow crew members on their fishing boat and fled to the South, the unification ministry said Thursday. They attempted to flee when the South's Navy tried to capture them, officials said.
"We made a decision to deport them after determining that accepting them to our society could pose a threat to the lives and safety of our people and that such criminals cannot be recognized as refugees under global law", Lee added.
Lee said the two were sent back through the Koreas' land border.
South Korea has a policy of accepting North Koreans who wants to resettle in the South to avoid political oppressions and economic poverty at home.
Mr Lee did not elaborate on why or how the two men had killed their colleagues.
But the investigation concluded that the men had killed 16 fishermen in their boat and then fled to South Korea, the Seoul Unification Ministry said. Their fishing boat will be sent back at a later date.
After being spotted by the South Korean navy, they attempted to abscond for two days despite warning shots from a South Korean navy vessel before being captured.
Observers say the men are likely to receive heavy punishment in North Korea, including possible execution.
"The government chose to expel them as they had committed grave, non-political crimes such as murder and were not subject to our protection under the law", South Korea's Unification Ministry spokesperson, Lee Sang-min said at a press briefing, according to Yonhap.
The trio later killed the 15 other fishermen one by one and threw their bodies overboard.
Unification Minister Kim Yeon-chul said at a separate parliamentary meeting the two North Koreans once expressed their willingness to defect, but there was no consistency in their statements.
About 32,000 North Koreans have fled to the South since the end of the Korean war, majority via China and in the past two decades. -South Korean military drills would amount to "throwing a wet blanket over the spark" of nuclear negotiations between Pyongyang and Washington.