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.
Mr 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 Mr 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 theas 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.