Kim Jong Nam, the estranged half brother of North Korean leader Kim Jong Un who was killed in Malaysia in 2017, was a CIA informant, the Wall Street Journal reported on Tuesday.
Citing "a person knowledgeable about the matter", the paper said Kim Jong Nam had met with CIA operatives several times.
Kim Jong Nam, who was once seen as heir apparent to the North's leadership, died after having his face smeared with the outlawed VX nerve agent as he waited at Kuala Lumpur airport.
According to the Journal's source there was a "nexus" between Kim Jong Nam and the CIA, but the paper said many details of his connection with the intelligence agency were unclear.
The source said Kim Jong Nam travelled to Malaysia in February 2017 to meet his CIA contact, but that may not have been the only purpose of his trip.
Kim Jong Nam died after being attacked at Kuala Lumpur International Airport on February 13, 2017 in a Cold War-style assassination that shocked the world.
Two young women, one Vietnamese and one Indonesian, were arrested and charged with the murder. They insisted they were tricked by North Korean agents into carrying out the hit and had thought it was a reality TV show prank.
Malaysian prosecutors eventually dropped the murder charges against them and Indonesian Siti Aisyah was released in March this year while her Vietnamese co-accused Doan Thi Huong was freed in May.
South Korea has accused the North of ordering the hit, which Pyongyang denies.
Once seen as leader Kim Jong Il's natural successor, Kim Jong Nam apparently fell from grace after being deported from Japan in 2001 for trying to enter on a forged passport to visit Disneyland.
Since then he had been living in virtual exile, mainly in the southern Chinese enclave of Macau.
He had spoken to Japanese and other overseas media with surprising candour on various occasions and 2011 he told a Japanese newspaper that he opposed the idea of the North's dynastic power transfer.
"Several former US officials said the half brother, who had lived outside of North Korea for many years and had no known power base in Pyongyang, was unlikely to be able to provide details of the secretive country's inner workings," the Journal said.
The report comes amid a deadlock in talks between the United States and North Korea over Pyongyang's nuclear weapons.
Kim Jong Un met US President Donald Trump for a historic first summit in Singapore last year but their second meeting in Hanoi in February this year collapsed when they failed to agree a deal on denuclearisation.