Kim Jong Un's half brother killed in Malaysia, sources report The oldest son of Kim Jong Il had been in line to succeed the late dictator.

SEOUL -- The half brother of North Korean leader Kim Jong Un was assassinated on Monday at the Kuala Lumpur International Airport, according to South Korean media outlets citing government sources.

Kim Jong Nam, the firstborn son of former North Korean leader Kim Jong Il, was sprayed with poison by two unidentified women who fled the scene in a taxi, according to the reports.

Malaysian police said in a statement today that a 46-year-old North Korean man "who sought initial medical assistance at the Kuala Lumpur International Airport" died Monday en route to a hospital.

Police said the man's travel document identified him as Kim Chol, a North Korean born on June 10, 1970. Kim Chol is the name of another brother of Kim Jong Un's, although South Korean government officials told South Korean media that the name in the passport was an alias for Kim Jong Nam.

The State Department told ABC News it was aware of the reports and referred questions about the death to Malaysian authorities. The South Korean Embassy in Washington told ABC News it did not have independent confirmation and was monitoring press coverage.

Many feared that Kim Jong Nam would be assassinated after Kim Jong Un took power in April 2012. A fierce rivalry between the two half brothers ran deep because of succession conflicts. Kim Jong Nam, as the eldest son in the family, had long been expected to rule North Korea after Kim Jong Il's death and was backed by senior Communist Party members, including Jang Sung Taek.

Jang, an uncle of the two rival brothers, had been considered No. 2 in power but was brutally executed a year after Kim Jong Un took power.

"North Korea is a society where you will be easily executed not because of your difference in political reasons but because of simple reasons — that you angered Kim Jong Un," said Thae Yong Ho, a former North Korean diplomat and the highest-level North Korean official to have defected to South Korea in two decades.

"North Korean society is just the reign of terror."

Kim Jong Nam reportedly fell out of favor in Pyongyang after being caught trying to enter Japan on a fake passport in 2001. He said he was heading to Tokyo Disneyland with his family. Since then, he had been in exile, moving discreetly among several countries, such as Singapore and Malaysia, as well as Macau, Hong Kong and other parts of China. His son, Kim Han Sol, was recently enrolled at Institut d'Etudes Politiques de Paris, according to South Korean media.

The two brothers never met in person, according to North Korea analysts in Seoul. But Kim Jong Un always regarded the outspoken Kim Jong Nam as a potential political threat.

For instance, Kim Jong Un built himself up in the image of his late grandfather and the founder of North Korea, Kim Il Sung, to gain popularity and to justify his accession to power. Kim Il Sung is still revered by the people as the pillar of the nation. From the moment he began appearing in public, Kim Jong Un has emphasized striking similarities with his grandfather like gaining weight, wearing the same eyeglasses and having an identical haircut. But it was Kim Jong Nam who grew up close to their grandfather.

The fact that Kim Jong Nam was born to the first legitimate wife of Kim Jong Il took a toll on Kim Jong Un, whose mother was Kim Jong Il's third wife, Koh Yong Hee, who came from a family that defected from North Korea to Japan — which is looked down on in a country where generations of loyalty to the regime is essential.

ABC News' Hong Yoo, from Seoul, and Conor Finnegan, from Washington, contributed to this report. Maureen Jeyasooriar contributed reporting from Kuala Lumpur.