Malaysian police have named a North Korean diplomat that they want to question in relation to the murder of Kim Jong-un’s estranged half-brother.

Police chief Khalid Abu Bakar said that 44-year-old Hyon Kwang Song, a second secretary at North Korea’s embassy, was wanted for questioning in connection with the death of Kim Jong-nam, who collapsed at Kuala Lumpur International Airport as he preparing to board a flight to Macau, China.

Investigators also want to interview Kim Uk Il, 37, an employee of the North Korean state-owned airline Air Koryo, he added.

Local media reports have suggested that both men are “hiding” in North Korea’s Malaysian embassy.

Kim Jong Nam death: Apparent CCTV of 'assassination' leaked

Mr Khalid said both men were in the country but he would not give details about their location.

The embassy had “been called in for assistance”, he said, adding: “We hope the embassy will cooperate with us and allow us to interview them quickly or else we will compel them to come to us.

“We can’t confirm that they are hiding in the embassy.”

A senior Malaysian security source, who did not want to be named, told The Telegraph that Hyon Kwang Song was “the supervisor of the whole plot”.

They said: “His role was to supervise all arrangements and report to the ambassador.”

Officials in South Korea and the US believe the killing was an assassination carried out by agents of the North.

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

Police have arrested four people in connection with the killing, including two female suspects, Doan Thi Huong, a 28-year-old Vietnamese citizen, and Siti Aisyah, 25, an Indonesian.

Mr Khalid said both women wiped a liquid, containing an as yet unidentified toxic substance, on Mr Kim’s face.

“The two female suspects knew that the substance they had was toxic. We don’t know what kind of chemical was used,” he said.

Dismissing claims that the women had thought they were taking part in a TV prank, he said the women had rehearsed the attack at two shopping centres in central Kuala Lumpur before assaulting Mr Kim.

“They used their bare hands,” he said, adding that they were instructed to wash their hands afterwards.

Kim Jong-un’s estranged half brother died at Kuala Lumpur airport after he collapsed while waiting to board a flight (AP)

Ri Jong-chol, a 47-year-old North Korean man, and Muhammad Farid bin Jalaluddin, the Malaysian boyfriend of Siti Aisyah have also been arrested.

Investigators have not stated Mr Ri’s role in the killing. He lived in Malaysia for three years without working at the company registered on his employment permit or receiving a salary.

Mr Khalid said police “strongly believed” four other suspects were back in the North Korean capital of Pyongyang, having fled Malaysia on the day of the attack.

Meanwhile, North Korea’s embassy issued a statement calling for the immediate release of the “innocent females”. It did not address the police request to interview one of its diplomats.

Security was also stepped up at the morgue where Mr Kim’s body is being held after an attempted break-in earlier this week, Mr Khalid said.

Malaysia has denied North Korea’s request for the body to be handed over to its embassy directly, saying it would be released to the next of kin, though none has come forward.

The investigation has strained Malaysia’s hitherto friendly relations with North Korea.