A North Korean national has been arrested over the killing of North Korean leader Kim Jong-un's half-brother, Malaysian police say.
The first North Korean to be arrested over Kim Jong-nam's death was named as Ri Jong Chol, 46.
An Indonesian woman, a Malaysian man and a woman with a Vietnamese passport were detained earlier.
Police believe poison was sprayed into Mr Kim's face as he waited to board a flight from Kuala Lumpur to Macau.
Malaysian Deputy Prime Minister Ahmad Zahid Hamidi formally confirmed on Thursday that the dead man, who was travelling under the name Kim Chol, was Kim Jong-nam.
Police say the latest suspect was detained on Friday evening in Selangor, near the Malaysian capital. No further details were given.
One of the detained women, an Indonesian national named as Siti Aisyah, is said to have told Malaysian police she had been paid to perform what she thought was a prank.
A Malaysian man thought to be her boyfriend was detained along with her.
The woman carrying a Vietnamese passport has been identified as Doan Thi Huong.
Kim is believed to have been attacked in the airport departure hall on Monday by two women, using some form of chemical.
A grainy image taken from security camera footage, which has been broadcast in South Korea and Malaysia, shows a woman wearing a white T-shirt with the letters "LOL" written on the front.
Police have now finished Kim Jong-nam's post-mortem examination, though the results have not yet been made public.
North Korea has said it will reject the result of the autopsy.
It has demanded that Malaysia immediately release the body. Malaysia is refusing to do so until it receives a DNA sample from Mr Kim's next-of-kin.
South Korea's intelligence agency has accused the country's rivals in the north of assassinating Kim Jong-nam, saying Pyongyang had wanted to kill him for years but that he was being protected by China.
Despite widespread speculation that North Korea was behind the killing, there has been no proof. Pyongyang has made no public comments on the issue.
Kim was largely estranged from his family, after being passed over for the North Korean leadership in favour of his youngest half-brother. He spent most of his time overseas in Macau, mainland China and Singapore.
He had spoken out in the past against his family's dynastic control of North Korea and in a 2012 book was quoted as saying he believed his younger half-brother lacked leadership qualities.
But he had said he was not interested in assuming the leadership himself.