Malaysia's police chief Khalid Abu Bakar said both officials were in Malaysia but could not confirm if they were in the North Korean embassy.

Malaysia has also requested Interpol to put an alert out to apprehend four North Korean suspects believed to have fled the country on the day of the murder.

So far, police have identified a total of eight North Koreans suspected of being linked to the killing. One is in custody.

Mr Khalid told reporters that a request had been made to Interpol to put out an alert to apprehend the four suspects, who they believe have already made their way back to North Korea.

The police chief also said the police have sent an official request to the North Korean embassy requesting to interview the embassy's second secretary and the airline official, having released their names on Wednesday.

"If you have nothing to hide, you should not be afraid to cooperate, you should cooperate," Mr Khalid told reporters.

Khalid said an arrest warrant will not be issued for the second secretary, as he has diplomatic immunity, but that "the process of the law will take place" if the airline official does not come forward.