Malaysia has asked for North Korea’s help in searching for a senior embassy official wanted in connection with the killing of Kim Jong-nam.
Kim, the half-brother of North Korean leader Kim Jong-un, died last week at Kuala Lumpur airport.
Police also confirmed details of the killing, saying two women approached him and wiped a toxin on his face.
There is widespread suspicion North Korea was behind the attack, which its envoy in Malaysia has angrily denied.
Speaking at a press conference in Kuala Lumpur on Wednesday, Malaysian Police Chief Khalid Abu Bakar said they were looking for three North Koreans in addition to the previously announced suspects.
One of them is Hyon Kwang Song, the second secretary of the North Korean embassy in Kuala Lumpur.
Khalid Abu Bakar said they had written to the North Korean ambassador to Malaysia asking him to allow police to interview Hyon and other suspects, which include a state airline worker.
If the ambassador does not co-operate, “we will compel them to come to us”, he said.
The police chief also said security had been stepped up at the morgue where Kim Jong-nam’s body is being kept after an attempted break-in earlier in the week.
“We knew there were attempts by someone to break into the hospital mortuary. We had to take precautions,” he was quoted by the Malay Mail as saying.
Ten people have either been named as suspects or are wanted by Malaysian police for questioning in connection to Kim Jong-nam’s killing.
•Doan Thi Huong, 28, Vietnamese, one of two women suspected of wiping toxins on Kim’s face. She is thought to be the woman seen in CCTV footage wearing a white top emblazoned with the letters “LOL”.
•Siti Aisyah, 25, Indonesian, the other female suspect. Indonesian authorities say she claims she thought she was taking part in a TV prank.
•Ri Jong Chol, 47, a North Korean.
•Hyon Kwang Song, 44, second secretary at the North Korean embassy in Kuala Lumpur. Believed to still be in Malaysia.
•Kim Uk Il, 37, staff member of North Korea’s state airline Air Koryo. Believed to still be in Malaysia.
•Ri Ju U, 30, a North Korean also known as James. Believed to still be in Malaysia.
•Ri Ji Hyon, 33, a North Korean. Believed to have fled to Pyongyang.
•Hong Song Hac, 34, a North Korean. Believed to have fled to Pyongyang.
•O Jong Gil, 55, a North Korean. Believed to have fled to Pyongyang.
•Ri Jae Nam, 57, a North Korean. Believed to have fled to Pyongyang.
Khalid Abu Bakar also confirmed widely reported details of the 13 February killing.
A leaked video of the incident shows a man resembling Kim being approached by one woman at Kuala Lumpur airport, before another woman lunges from behind and grabs his face.
Khalid said the two female suspects had wiped a toxin on Kim’s face with their bare hands and after that they went away.
Indonesian authorities have said Siti Aisyah had thought she was taking part in a TV prank, but Khalid said the women had clearly been “instructed to clean their hands” and that they knew the substance was toxic.
He added that the women practised the move several times beforehand in shopping centres in Kuala Lumpur.
Authorities are still waiting for the results of the post-mortem examination of Mr Kim’s body, and are seeking his family members to provide a DNA sample.
North Korea has demanded that Kim’s body be returned to them, and has angrily objected to Malaysia conducting an autopsy of the body.
Malaysia has cited the need to carry out an investigation as Kim died on their soil.
Relations between the two countries have become strained over the incident, with North Korea’s ambassador to Malaysia saying he did not trust the police investigation and Kuala Lumpur recalling its envoy in Pyongyang.