A female Indonesian suspect and a Malaysian man thought to be her boyfriend were both detained on February 16.
A woman travelling on a Vietnamese passport has also been detained.
Kim Jong-nam died on February 13 after apparently being poisoned while waiting to board a flight in Kuala Lumpur.
Malaysian police say they have now finished their post-mortem examination, though the results have not yet been made public.
The two female suspects have been remanded in custody for seven days.
The inspector general of the Royal Malaysia police, Sri Khalid Bin Abu Bakar, said the second woman was detained on February 16 over the death of “a Korean male”.
She was identified from airport CCTV footage and had an Indonesian passport.
Malaysian Deputy PM Ahmad Zahid Hamidi formally confirmed today that the dead man, who was traveling under the name Kim Chol, was Kim Jong-nam, according to state news agency Bernama.
There is widespread speculation that North Korea was behind the killing, but there has been no proof.
On February 16, North Korea is celebrating what would have been the 75th birthday of Kim Jong-il, the late leader and father of both Kim Jong-nam and Kim Jong-un.
On February 15, Kim Jong-un was seen attending a ruling party meeting. Footage aired on state media showed him grim-faced, reported South Korea’s Yonhap news agency, and he did not wave when he left, as is customary.
Kim Jong-nam is believed to have been attacked in the airport departure hall 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.
It is not clear whether either is the woman in the footage, and police say they are still looking for “a few” other suspects.
Malaysia police said the woman arrested on February 16 was identified in her passport as Siti Aishah, 25, from Banten province in Indonesia.
The suspect arrested on February 15 had Vietnamese travel documents bearing the name Doan Thi Huong, 28.
Kim Jong-nam was largely estranged from his family, after being bypassed for inheriting the leadership in favor of his youngest half-brother.
He spent most of his time overseas in Macau, mainland China and Singapore.
Kim Jong-nam 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.
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