Rights group Lawyers for Liberty (LFL) has called for an explanation by the home minister of the nearly 300 deaths that occurred in immigration depots since 2020, calling the disclosure "shocking and disturbing".
In a statement, LFL highlighted the deaths of six children among the 298, saying an immediate inquest must be held to determine the cause.
"It is alarming that despite there having been hundreds of deaths in the immigration depots within a short span of time, there have been no inquest proceedings instituted regarding any one of them," it said.
"What were the causes of death? Was the local magistrate informed, and if not, why? Are the authorities not interested in finding out?"
Home Minister Hamzah Zainudin had said on July 20 that 264 of the detainees who died were men while 34 were women.
Speaking in the Dewan Rakyat, he said 154 deaths involved Indonesian and Filipino detainees at immigration depots in Sabah.
LFL director Zaid Malek said Hamzah had offered no explanation for the hundreds of deaths, adding that the minister was behaving "as if such deaths are routine and require no explanation to the public as well as to the families of the victims or the nations from which they came".
"This revelation comes almost a month after his callous comment regarding the reported deaths of nearly 150 Indonesians in detention centres in Sabah, in which he simply brushed it off as a normal occurrence, saying flippantly 'It would be great if I had the ability to know when someone is about to die'," Zaid added.
Citing Sections 329 and 330 of the Criminal Procedure Code, he said it was the duty of the police to investigate such deaths and order post-mortem examinations.
"Deaths in custody are a serious matter and cannot simply be brushed off without a proper investigation, and especially so when they number in the hundreds," he said.
Adding that the government had a duty to ensure the safety and well-being of all, regardless of citizenship, he said it was not enough to propose "shallow solutions" such as improving the deportation process to avoid overcrowding.
"The cause of death must be ascertained, and improvements, reparations or criminal proceedings must be taken against any person liable by act or omission in the death of any detainee."
Zaid also referred to Indonesia's move to freeze the entry of its citizens into Malaysia, saying the unexplained deaths would only worsen Malaysia's ties with the republic and other countries whose citizens have died in Putrajaya's custody.
He likewise cited the latest Trafficking in Persons report by the US Department of State, saying it was "no surprise" that Malaysia had remained on the lowest tier for yet another year.