Kim Jong Nam, the older half-brother of the North Korean leader, was known to be based mostly outside of his home country.
South Korea’s TV Chosun, a cable television network, said that Kim was poisoned at Kuala Lumpur airport by two women believed to be North Korean operatives, who were at large, citing multiple South Korean government sources.
The South Korean government source who spoke to Reuters did not immediately provide further details.
South Korea’s foreign ministry said it could not confirm the reports, and the country’s intelligence agency could not immediately be reached for comment.
The police chief in charge of Kuala Lumpur International Airport, Assistant Commissioner Abdul Aziz Ali, told Reuters a Korean in his forties was found sick at the airport on Monday.
Airport authorities rushed him to the hospital and he died on the way, the police chief said.
“We do not have any other details of this Korean man. We do not know his identity,” Abdul said.
An employee in the emergency ward of Putrajaya hospital said a deceased Korean there was born in 1970 and surnamed Kim.
Kim Jong Nam was once considered heir apparent but fell out of favour with his father Kim Jong Il following a botched attempt in 2001 to enter Japan on a forged passport and visit Disneyland.
He has since lived in virtual exile, mainly in the Chinese territory of Macau.
Kim Jong Un took over as North Korean leader when his father died in December 2011.
Kim Jong Nam, known as an advocate of reform in the North, once told a Japanese newspaper that he opposed his country’s dynastic power transfers.
If confirmed, Kim’s case would be the highest-profile death under the Kim Jong Un regime since the execution of the leader’s uncle Jang Song Thaek in December 2013.