Image copyright AP Image caption Kim Jong-nam, the North Korean leader's half-brother, was killed by unknown assailants in Kuala Lumpur

South Korea has said it believes the North Korean regime is involved in the murder of Kim Jong-nam.

North Korean leader Kim Jong-un's half-brother was killed at Malaysia's Kuala Lumpur airport last week.

"We believe the North Korean regime is behind this incident considering five suspects are North Koreans," said Seoul's unification ministry spokesman.

Malaysian police have already detained one North Korean and they say they are looking for four more.

Despite widespread speculation that North Korea was behind the killing, there has been no proof. Pyongyang has made no public comments on the issue.

Image copyright AFP Image caption North Korea's Kim Jong-Un has not made a statement about his half-brother's death

Deputy national police chief Noor Rashid Ismail identified the latest North Korean suspects in a press conference on Sunday.

He named them as Ri Ji Hyon, 33; Hong Song Hac, 34; O Jong Gil, 55, and Ri Jae Nam, 57.

He said the men left on 13 February, the day Kim was killed, and had arrived on different days within the previous fortnight.

"I am not going to disclose where they are," said Mr Noor Rashid, but confirmed that his force was working with world police body Interpol.

He said they held normal, not diplomatic, passports.

Image copyright AFP Image caption Kim Jong-nam had been critical of the North Korean government

Malaysian police believe poison was forced into Kim's face as he waited to board a flight to Macau.

They say Kim sought help at an airport customer service desk before he died.

Mr Noor Rashid said Kim told the desk that "two unidentified women had swabbed or had wiped his face with a liquid and that he felt dizzy".

What's happening to Kim's body?

Malaysian police are still waiting for the results of an autopsy conducted on Wednesday.

Malaysia's health minister said it could take around two weeks to receive the toxicology report.

North Korea has said it will reject the results of the autopsy.

Pyongyang has also demanded Kim's body be returned to North Korea, but Malaysia says it has to conduct DNA testing first and needs a sample from another family member.

"We are trying very hard to get the next of kin to come and assist us in the investigation," said Mr Noor Rashid.

Who has been arrested in Malaysia?

Four other people have already been detained in connection with Kim's death.

They are: North Korean man Ri Jong Chol, a Malaysian man, Muhammad Farid Bin Jalaluddin, a woman with a Vietnamese passport in the name of Doan Thi Huong and an Indonesian woman.

The Indonesian, who was named as Siti Aisyah, is said to have told Malaysian police she had been paid to perform what she thought was a prank.

Image copyright REX/Shutterstock Image caption This CCTV image has been broadcast by South Korean and Malaysian media

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 one of the suspects wearing a white T-shirt with the letters "LOL" written on the front.

Who was Kim Jong-nam?

Kim was the first-born son of former North Korean leader Kim Jong-il, who died in 2011.

He was largely estranged from his family, after being passed over for the North Korean leadership in favour of his youngest half-brother.

He went into exile in the early 2000s, spending most of his time in Macau, mainland China and Singapore.

Image copyright Getty Images Image caption Deceased North Korean leader Kim Jong-il (left) with his first-born son Kim Jong-nam (right) in a 1981 family photo

Kim 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.