North Korean leader Kim Jong-un’s half-brother was an informant for the US Central Intelligence Agency before he was assassinated in Malaysia, it has been claimed.

The report of a “nexus” between the CIA and Kim Jong-nam, 45, surfaced in the Wall Street Journal on Monday, citing an unnamed “person knowledgeable about the matter.”

However, the claim was first reported last week in The Times, based on a new book by Anna Fifield, a Washington Post journalist, which alleges that Kim was not only a CIA informant but that he laundered counterfeit money through casinos and associated with gangsters.

The book sheds new light on the possible reasons for Kim’s gruesome murder in February 2017 in Kuala Lumpur airport, when he was smeared with lethal VX agent by two women who thought they were taking part in a reality TV prank show.

The US and South Korea have accused the North Korean regime of orchestrating the audacious assassination, although Pyongyang denies the accusation.

Donald Trump said he would not have allowed US intelligence to use Kim Jong-un's half-brother as an asset.

Asked about the CIA's links to Kim Jong-nam, Mr Trump said: "I don't know about that... I know that the relationship is such that that wouldn't happen under my auspices."

Mr Trump also said he had received another "beautiful letter" from the North Korean leader and expressed openness to a third summit with him. Mr Trump said Kim had "kept his word" and "that's very important to me."

Kim, who lived in exile in Macau before he died, was reportedly viewed as a threat to the rule of his ruthless younger brother, and any meetings with American spies would have added to that paranoia.

“Kim Jong-nam became an informant for the CIA, an agency with a track record of trying to bring down dictators it didn’t like,” Ms Fifield writes in The Great Successor: The Secret Rise and Rule of Kim Jong Un.

Kim Jong-nam and Kim Jong-un remained estranged as adults Credit: Shizuo Kambayashi/AP

“His brother would have considered talking to American spies a treacherous act,” she adds. “Kim Jong-nam provided information to them, usually meeting his handlers in Singapore or Malaysia.”

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The Journal source said that Kim had travelled to Malaysia in February 2017 to meet his CIA contact, although this may not have been the sole reason for the trip.

Former officials said that he had almost certainly been in contact with security services from other countries, particularly China’s, although he had no known power base in Pyongyang and had not lived in the country for several years.

As the eldest son of the Kim dynasty, Jong-nam was groomed for years as the successor to his father Kim Jong-il before he fell out of favour after the arrival of his three younger siblings.

The tipping point into disgrace was reportedly a surreptitious trip to Japan on a fake passport to visit Disneyland, after which he left his homeland and, according to the book, lived in the shadows “amid gamblers, gangsters and spies.”

Kim spent time in Macau and Singapore, using multiples aliases. He had a Portuguese and Chinese passport as well as two North Korean ones in different names, including Kim Chol.

Meanwhile, his former privileged position in the family’s hereditary dynasty was overtaken by his youngest half-brother, Kim Jong-un, who assumed power shortly after their father’s death in December 2011.

Jong-nam, born to a North Korean starlet, and Jong-un to Ko Yong Hui, a dancer, had experienced isolated childhoods, and both were educated separately in Switzerland.

The brothers remained estranged as adults, and in 2013 the younger Kim executed Chang Song-thaek, his aunt’s husband, who was said to be close to Jong-nam.

The execution heightened Jong-nam’s fears that he was living on borrowed time, according to friends, although he is not believed to have been travelling with bodyguards at the time of his death.

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