Kuala Lumpur, Malaysia (CNN) Malaysian authorities want to speak with a North Korean embassy official and airline employee as part of their investigation into the murder of Kim Jong Nam.

The two being sought are Hyon Kwang Song, who worked at the North Korean embassy in Malaysia, and Kim Uk Il, a staff member of the North Korean carrier Air Koryo, Malaysian Inspector-General of Police Khalid Abu Bakar told a Wednesday news conference. Both are still in Malaysia, he said.

Kim Jong Nam was the estranged half-brother of North Korean leader Kim Jong Un. He died last Monday after a suspected poisoning while trying to catch a flight from Kuala Lumpur to Macau.

Security has been increased at the morgue where Kim Jong Nam's body is being held after an attempted break-in, Bakar told reporters.

But he wouldn't be pushed on whether the break-in suspects were North Korean.

"We know who they are. No need to tell you," he said.

Royal Malaysian Police Special Forces personnel stand guard inside the compound of the forensic wing at Hospital Kuala Lumpur in the early hours of Tuesday, where the body of a North Korean man suspected to be Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong Un, is being kept.

Uncooperative

In addition to the embassy worker and airline employee, Malaysian authorities are looking for four North Korean suspects, who they "strongly believe" are back in Pyongyang.

Police say they are seeking another North Korean -- named as 30-year-old Ri Ji U -- to assist them with the investigation. Ri is still thought to be in Malaysia.

Bakar said that North Korean authorities had not complied with requests to hand over the suspects in Pyongyang, or offered assistance to help the Malaysians interview Hyon Kwang Song and Kim Uk Il.

If Kim and Hyon do not come forward, police will seek arrest warrants for them, Bakar said.

"We are being very fair in the investigation and they should assist us," he said.

Bakar also shot down the idea of a joint investigation with the North Koreans, saying it's not their jurisdiction.

Prank story dismissed

Police are seeking to hold three suspects in custody longer for questioning. They are 46-year-old Ri Jong Chol of North Korea, 25-year-old Siti Aishah of Indonesia, and 28-year-old Doan Thi Huong of Vietnam.

A fourth, 26-year-old Muhammad Farid Bin Jalaluddin, will be released Wednesday on bond, Bakar said. Jalaluddin was Aishah's boyfriend.

In one of the stranger twists in the case, Indonesian police said last week that Aishah told them she not aware that she was part of a murder plot. She thought it was participating in a prank for a TV show.

But Bakar said Malaysian authorities aren't buying that excuse -- he says the women were trained, pointing in part to security footage that surfaced Monday which appeared to show the assault.

"These two ladies were trained to swab the deceased's face," he said.

JUST WATCHED Authorities describe Kim Jong Nam killing suspect's actions Replay More Videos ... MUST WATCH Authorities describe Kim Jong Nam killing suspect's actions 03:14

Police believe the four suspects who are now in Pyongyang gave a liquid substance to Aishah and Huong.

Aishah did it first, followed by Huong. They both then went to the restroom to wash their hands, as they were instructed to by the four North Koreans.

"They knew it was toxic," Bakar said. "Of course they knew."

JUST WATCHED Video appears to show Kim Jong Nam attacked Replay More Videos ... MUST WATCH Video appears to show Kim Jong Nam attacked 01:28

Bad relations getting worse

The North Korean embassy in Malaysia issued a statement Wednesday accusing investigators of "unreasonably" arresting Ri and calling for the release of all three suspects in custody.

It said Aishah and Huong could not have used poison because they did not die themselves.

The statement also repeated previous accusations that Malaysian investigators were siding with South Koreans -- a charge previously made by Pyongyang's ambassador to Malaysia, Kang Chol.

Malaysia insists it's following standard protocol when it comes to a murder investigation.

However, North Korea says Malaysia's demands for DNA to confirm the victim's identity suggest that investigators don't trust the North, which is "insulting to the sovereignty" of North Korea.

Wednesday's back-and-forth is the latest nadir in the already-souring relationship between the two countries.

On Monday, Malaysia summoned Kang and recalled its ambassador to North Korea , in response to the ambassador's accusation that investigators were conspiring with "hostile forces."

Kang Chol, North Korea's ambassador to Malaysia, walks to address journalists outside the North Korean Embassy in Kuala Lumpur on Monday, February 20.

"The statement by the ambassador was totally uncalled for, it is considered diplomatically rude on his part," Malaysian Prime Minister Najib Razak said Tuesday in response.

"It is incumbent upon us to find out the truth about the crime and they should help us to find out the truth. That is more important than making sweeping and baseless statements, because Malaysia is not the pawn of any country and we will never be the pawn of any country."

For the first time on Thursday, North Korean state media reported on the death, claiming the unnamed North Korean citizen died of "heart stroke."

The report accused South Korea of fabricating the poisoning story, and criticized Malaysia for responding to it.

"The biggest responsibility for his death rests with the government of Malaysia as the citizen of the DPRK died in its land," the report added.

Kim who?

Malaysian Police Inspector-General Bakar also denied rumors Wednesday that Kim Jong Nam's son had come to the country to collect his father's body.

He would not confirm that the body belonged to Kim Jong Nam, referring to him instead by the name Kim Chol.

Malaysia's Deputy Prime Minister said last week North Korean embassy in Malaysia confirmed Kim Jong Nam's identity. He added that Kim Jong Nam, who had a reputation for traveling with false documents, had been traveling with two passports -- one under the name Kim Chol.

Datin Asmawati Binti Ahmad, head of Malaysian police corporate communications, told CNN one of the two passports Kim was carrying was diplomatic, but he didn't specify which one. North Korea state media also reported the dead man was carrying a diplomatic passport.

Royal Malaysian Police Inspector-General Khalid Abu Bakar addresses journalists on Wednesday, February 22.

Police are waiting for DNA to officially announce the dead man's identity. They've asked the North Korean embassy to help them get a sample from next-of-kin, a request that Ambassador Kang called "preposterous."

North Korea opposes any autopsy that is done without their own officials present and has publicly demanded the return of Kim Chol's body.

The Malaysians say that without DNA from a next of kin, Malaysia won't hand over Kim's body or release the autopsy report, which could reveal the cause of death.

If next-of-kin do arrive, they would be provided police protection, Bakar said.

CORRECTION: This story has been updated to accurately reflect the number of suspects Malaysian officials are searching for in connection to their investigation.