The death of a Palestinian man while in the custody of the Gaza government in recent weeks must be thoroughly and transparently investigated, human rights groups say.

Atef Khamis Derbas, 52, was being held in the central Ansar prison in Gaza City for unpaid debts, before he died on Dec. 27.

His family told the Al-Haq human rights group they had informed prison authorities of his pre-existing medical problems, and that he was suffering in jail due to cold conditions and not taking his medication regularly.

A representative of Al-Haq told Ma'an an official investigation was opened by Gaza authorities on Monday.

Derbas' family strongly believe Atef died due to medical negligence and poor conditions in jail, al-Haq said. The autopsy report received by the family says the main cause of death was heart failure.

Al-Haq said it had "grave concern at the number of deaths occurring inside Palestinian prisons." On Oct. 16, 27-year-old Mohammad Said Al-Zaqzouq man died in police custody in Khan Younis, south Gaza.

Police said he had committed suicide, and a police source told the Palestinian Center for Human Rights that officers gave him the blanket with which he later strangled himself.

Meanwhile, the Palestinian Center for Human Rights called for a "serious and thorough investigation" into Derbas' death, urging the government to publish the findings publicly. 

"The Palestinian Authority is responsible for the life of all the prisoners and detainees being held in its prisons; thus, it is responsible for protecting their dignity, as well as providing adequate medical care for them, in accordance with Reform and Rehabilitation Centers Law of 1998," the group said.