Officials from the Unification Ministry in Seoul said the men, both in their 20s, illegally breached the inter-Korean maritime frontier off the east coast aboard a squid boat. An investigation by South Korean authorities who detained the fishermen for questioning found they had fled to the South after killing 16 other men on the vessel and dumping their bodies in the sea.
Unification Ministry spokesman Lee Sang-min said: “The government decided to expel them as they had committed grave, non-political crimes such as murder and were not subject to our protection under the law.
“We also assessed that if they were accepted into our society, they would pose danger to our people’s lives and safety as vicious criminals who cannot be recognised as refugees under international law.”
The fishermen were handed over to North Koran officials at the border village of Panmunjom in the demilitarised zone (DMZ) dividing North and South Korea.
Mr Lee did not elaborate on why or how the two men had killed their colleagues.
But Defence Minister Jeong Kyeong-doo told a parliamentary session that there was an “unfortunate event” between the sailors due to an abusive captain.
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.
READ MORE: Kim’s elite hackers launch attack on India’s nuclear weapons systems
Opposition MPs accused the government of concealing the incident, which was only revealed by a local media image of a presidential official reading a text message from a military officer saying the two men would be returned.
The photo prompted the ministry to hold an unscheduled news conference after the men were expelled.
North Korean fisherman regularly leave their own waters to operate illegally farther afield.
A North Korean fishing boat was confronted in the Sea of Japan by a Coast Guard vessel last month and the encounter ended with the Korean ship being sunk after a collision.
The Coast Guard rescued 60 North Koreans but there was no way to confirm they had been illegally fishing within Japan’s exclusive economic zone (EEZ) – as their boat had sunk.
The crew were put aboard other North Korean vessels and told to leave.