Security is high at the mortuary in Kuala Lumpur holding the body of Kim Jong-nam, the estranged half brother of North Korea's leader Kim Jong-un.
Mr Kim died last week after apparently being poisoned while waiting for a flight at a Kuala Lumpur airport.
There is growing speculation that his son, Kim Han-sol, has travelled to Malaysia to claim the body.
In a growing diplomatic row, Malaysia refused a request from the North Korean embassy to hand over the remains.
It wants a member of the Kim family to provide a DNA sample so his identity can be confirmed before the body is released.
A post-mortem examination has been conducted, despite North Korean objections, and the results are expected to be released this week.
In the early hours of Tuesday morning, heavily armed police arrived at Hospital Kuala Lumpur, where the body is being held, followed by several unmarked vehicles.
There has been no official confirmation that Kim Han-sol is in Malaysia, but there is widespread speculation in Malaysian media that he arrived in the country on Monday night, from Macau.
Little is known about Han-sol, who is Mr Kim's oldest son. The family have maintained a low profile life since falling out of favour with the North Korean regime, but he is believed to be academically gifted and to live in either Macau or France.
Meanwhile, Malaysia has said it is "insulted" by comments from North Korea's ambassador, Kang Chol, who accused Kuala Lumpur of a cover-up.
"It has been seven days since the incident but there is no clear evidence on the cause of the death and at the moment we cannot trust the investigation by the Malaysian police," he told reporters.
"It only increases the doubt that there is someone else's hand behind the investigation."
Malaysia's Foreign Minister Anifah Aman said the diplomat's allegations were based on "delusions, lies and half-truths". Mr Kang has been summoned to explain his comments.
Malaysia has also recalled its ambassador to Pyongyang, Mohamad Nizan Mohamad, over the killing.
So far, four people have been arrested in connection with the killing - identified as being from North Korea, Malaysia, Indonesia and Vietnam - and at least four North Koreans are being sought by investigators.
Despite widespread speculation that North Korea was behind the killing, there has been no definitive evidence and Pyongyang is yet to issue an official statement.
South Korea has accused the North of orchestrating the incident, saying on Monday it was evidence of North Korean "terrorism getting bolder".