He was believed to be in his mid-40s.
Police in Malaysia told Reuters on Tuesday an unidentified North Korean man had died en route to hospital from Kuala Lumpur airport on Monday. Abdul Aziz Ali, police chief for the Sepang district, said the man's identity had not been verified.
An employee in the emergency ward of Putrajaya hospital said a deceased Korean there was born in 1970 and surnamed Kim.
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.
Malaysian police have detained a woman holding Vietnam travel papers and are looking for a "few" other foreign suspects in connection with the assassination.
Lawmakers in South Korea had earlier cited their spy agency as saying it suspected two female North Korean agents had murdered Kim Jong Nam, and U.S. government sources also told Reuters they believed North Korean assassins were responsible.
The woman detained at Kuala Lumpur airport was identified from CCTV footage at the airport and was alone when she was apprehended, police said in a statement.Media had earlier published a grainy CCTV-captured image of a young woman wearing a white shirt with the letters "LOL" on the front.
Documents she carried were in the name of Doan Thi Huong, showed a birth date of May 1998 and birthplace of Nam Dinh, Vietnam, police said.
South Korean intelligence believes Kim Jong Nam was poisoned, the lawmakers in South Korea's capital, Seoul, said.
The spy agency told them that the young and unpredictable North Korean leader had issued a "standing order" for his half-brother's assassination, and that there had been a failed attempt in 2012.
"The cause of death is strongly suspected to be a poisoning attack," said South Korean lawmaker Kim Byung-kee, who was briefed by the spy agency.
The U.S. government strongly believes that North Korean agents murdered the estranged half-brother of North Korean leader Kim Jong Un in Malaysia, U.S. government sources said on Tuesday.
American authorities have not yet determined exactly how Kim Jong Nam was killed, according to two sources, who did not provide specific evidence to support the U.S. government's view.
South Korea's spy agency, however, suspects two female North Korean agents assassinated the estranged half-brother of North Korean leader.
South Korean intelligence believed Kim Jong Nam was poisoned, lawmakers said after being briefed by the spy agency.
They said the spy agency told them that the young, unpredictable North Korean leader had issued a "standing order" for his half-brother's assassination, and that there had been a failed attempt in 2012.
According to South Korea's spy agency, Kim Jong Nam had been living, under Beijing's protection, with his second wife in the Chinese territory of Macau, the lawmakers said. One of them said Kim Jong Nam also had a wife and son in Beijing.
Portly and gregarious, Kim Jong Nam was the eldest son of late North Korean leader Kim Jong Il and had spoken out publicly against his family's dynastic control of the isolated state.
"If the murder of Kim Jong Nam was confirmed to be committed by the North Korean regime, that would clearly depict the brutality and inhumanity of the Kim Jong Un regime," South Korean Prime Minister Hwang Kyo-ahn, who is also acting president, told a security meeting.
The meeting was called in response to Kim Jong Nam's death, news of which first emerged late on Tuesday.
South Korea is acutely sensitive to any sign of instability in isolated North Korea, and is still technically in a state of war with its impoverished and nuclear-armed neighbor, which carried out its latest ballistic missile test on Sunday.
Kim Jong Nam was believed to be close to his uncle, Jang Song Thaek, who was North Korea's second most powerful man before being executed on Kim Jong Un's orders in 2013.
In 2001, Kim Jong Nam was caught at an airport in Japan traveling on a fake passport, saying he had wanted to visit Tokyo Disneyland. He was known to travel to Hong Kong, Macau and mainland China.
He said several times over the years that he had no interest in leading his country.
"Personally I am against third-generation succession," he told Japan's Asahi TV in 2010, before his younger had succeeded their father.
"I hope my younger brother will do his best for the sake of North Koreans' prosperous lives."