To carry out the order, officials from the ministry met Kim Jong-nam in Macau on Jan. 20 and Kim asked them to give him some time to think about the younger brother's request, according to the report.

"Kim Jong-un was apparently worried about Kim Jong-nam fleeing to the United States or South Korea out of fear of being killed," the official was quoted as saying. "Kim Jong-un is believed to have ordered that Kim Jong-nam to be assassinated before he sought asylum overseas."

A source with knowledge of North Korean affairs told RFA that Kim Jong-un had the North's diplomats overseas meet Kim Jong-nam twice -- late last year and early this year. On a separate occasion, a North Korean official stationed in Laos gave Kim Jong-nam a letter from the current leader after meeting him in person, the source said.

The leader is believed to have attempted to cajole him into returning home, but Kim Jong-nam's failure to give a definite answer apparently led to the fratricidal order, according to the source.

Kim was killed on Monday at Kuala Lumpur International Airport after being attacked by two unidentified women with poison. Seoul's spy agency on Wednesday confirmed the killing of Kim, stopping short of saying that North Korea was behind the latest killing.

But it said that the murder of Kim Jong-nam has been a "standing order" issued by Kim Jong-un since he inherited power in late 2011 following the sudden death of his father.

Kim Jong-nam -- the eldest son of Kim Jong-il -- was once an heir apparent, but he had been living in foreign countries for years after apparently falling out of favor with his father for attempting to enter Japan with a fake passport in 2001. (Yonhap)