Kim Jong-un’s brother had begged the North Korean leader to spare his life before he was “assassinated” in Malaysia, intelligence officials have revealed as police arrested a second and third suspect in connection with the death.

Kim Jong-nam, 45, wrote a letter to his brother in 2012, who took power after their father Kim Jong-il died in 2011, pleading with him to withdraw a standing order for his assassination, according to lawmakers who were briefed by South Korea’s spy agency.

It comes following two further arrests in connection with Mr Kim's death, thought to have involved a poisonous liquid being sprayed into his face at Kuala Lumpur international airport on Monday as he prepared to board a flight to Macau, causing him to suffer a seizure which led to his death.

A second woman holding an Indonesian passport that identified her as 25-year-old Siti Aishah was detained on Thursday, while the third suspect, believed to be the boyfriend of one of the arrested women, was reportedly arrested on the same day but has not yet been named.

The first suspect, who held Vietnamese documents bearing the name Doan Thi Huong, aged 28, was arrested on Wednesday after she was “positively identified from the CCTV footage at the airport and was alone at the time of arrest”. Both female suspects have reportedly been remanded in custody in Malaysia for seven days.

Lee Byung-ho, head of the National Intelligence Service, told MPs in Seoul on Thursday that the North Korean intelligence services had been “consistently preparing for the killing” of Mr Kim, who had previously referred to the North Korean regime as “a joke” and predicted that it would soon collapse.

“It was a command that had to be pulled off, no matter what. The [North Korean] spy agency had consistently been preparing for the killing and they accomplished it this time,” Mr Byung-ho said

A member of the parliamentary intelligence committee in South Korea, Kim Byung-kee, said that there had been an assassination attempt against Mr Kim five years ago, according to The Times.

CCTV shows woman arrested in connection with Kim Jong-nam murder wearing LOL t-shirt

“In April 2012 Kim Jong-nam sent a letter to Kim Jong-un, begging for mercy for him and his family and saying they had no place to hide, and they understood very well that the only way to escape was to commit suicide,” said Mr Byung-kee.

MPs were told by intelligence officers the North Korean leader had said: "I just hate him, so get rid of him."

The letter from Mr Kim addressed to his brother reportedly read: “We have nowhere to go, nowhere to hide. We are well aware that the only way to escape is suicide.”

CCTV footage circulating the internet on Wednesday showed a woman suspected to be one of the attackers in Kuala Lumpur airport wearing a short skirt and a long-sleeved shirt with the letters “LOL” — an acronym for “laughing out loud” written across it.

A post-mortem examination carried out at a hospital in Kuala Lumpur on Wednesday despite objections from diplomats at the North Korean embassy, who had requested the examination did not take place at that the body be released immediately. It is not clear when the results of the post-mortem will be made public.

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Police added yesterday that he had been grabbed from behind and sprayed or splashed in the face with an unidentified liquid.

Just prior to his death, Mr Kim “felt like someone grabbed or held his face from behind”, according to a Malaysian police official, before he suffered a “mild” seizure subsequently died in an ambulance on the way to hospital.

There has reportedly been no mention of Mr Kim's killing in North Korea's official media.