Malaysia also recalled its envoy to Pyongyang after a spat erupted when North Korean demands to hand over the body of Kim Jong-nam were rejected.
"The ministry emphasised that as the death occurred on Malaysian soil under mysterious circumstances, it is the responsibility of the Malaysian government to conduct an investigation to identify the cause of death," a foreign ministry statement said after a meeting with the North Korean ambassador.
Ambassador Kang Chol last week accused Malaysia of colluding with "hostile forces" to damage the North, after rival South Korea said Pyongyang had orchestrated the airport attack.
Malaysia views the complaint as "baseless", the foreign ministry statement said.
"The Malaysian government takes very seriously any unfounded attempt to tarnish its reputation," it said. "The Malaysian ambassador in Pyongyang has been recalled to Kuala Lumpur for consultations."
North Korea cannot trust the Malaysian police investigation into the death, Pyongyang's ambassador said Monday after being summoned.
"It has been seven days since the incident, but there is no clear evidence on the cause of death and at the moment we cannot trust the investigation by the Malaysian police," Kang told reporters outside the embassy.
Police had "pinned the suspicion on us", he added, calling on Malaysia and the international community to work with North Korea on a joint investigation.
CCTV footage purportedly showing the deadly assault in Malaysia on Kim Jong-nam by a woman - who is believed to have wiped a fast-acting poison on his face - was released on Monday.
Kim Jong-nam died last Monday a short time after the attack in the departure hall of Kuala Lumpur International Airport, where he had been preparing to take a flight to Macau.
Malaysian police have detained four suspects - a Vietnamese woman, an Indonesian woman, a Malaysian man, and North Korean man - and are on the hunt for four other North Koreans who fled the country on the day of the attack.
At least three of four North Korean men wanted in connection with the murder caught a flight from Jakarta, Indonesia to Dubai on the evening of the attack, Indonesian immigration office spokesman Agung Sampurno told Reuters news agency by text message. The details of the fourth suspect were unclear.
The grainy closed-circuit television footage showed from two different angles a woman wearing a white top grab a man's face from behind with both hands and walk away.
A second woman was also seen walking swiftly away in another direction after the assault, though it was unclear if she had participated in the attack.
The portly, balding, middle-aged man was seen stumbling and wiping his face after the assault, and later clips showed him seeking help from people while gesturing to his face and then being escorted to a clinic.
More footage showed him inside the clinic seeking medical assistance.
The authenticity of the video could not independently be verified, and police officials were not immediately available for comment.
In a press conference on Sunday, the police said the victim complained to the airport customer service personnel that two women had "wiped his face with a liquid".
Autopsy results could be released as early as Wednesday, Malaysia's health minister said on Monday.
"We are talking about the normal period of time to complete most post mortem and give results, so on this basis, yes," Health Minister Subramaniam Sathasivam told reporters in response to a question about when results would be released.
North Korean officials have sought to prevent Malaysia from carrying out an autopsy and demanded the body be handed over directly.
South Korean Prime Minister Hwang Kyo-ahn told a meeting of South Korea's National Security Council on Monday it was nearly certain that North Korea was behind the killing of Kim Jong-nam, the eldest son of the late North Korean leader Kim Jong-il.
Kim Jong-nam, 46, who had been living in the Chinese territory of Macau under Beijing's protection, had spoken out publicly against his family's dynastic control of the isolated, nuclear-armed nation.
Source: News agencies