Hundreds of Palestinians are being held in detention centres in southern Israel, having been arrested in military operations across the Gaza Strip since its war with Hamas militants erupted on October 7.

"The Israeli military must urgently disclose the fate and whereabouts of everyone that it has detained since 7 October," Heba Morayef, Amnesty's regional director for the Middle East and North Africa, said in a statement.

"Israeli forces must specify the grounds of arrest for those detained and make every effort to provide families of those in its custody with information, particularly in light of the telecommunications blackouts that have cut off Gazans."

Amnesty demanded an investigation into the "inhumane treatment and enforced disappearance" of the detainees from Gaza.

The Israeli army on Tuesday said it was investigating the deaths of detainees arrested in Gaza.

It did not provide details regarding how many detainees had died or the circumstances of their deaths.

On Tuesday Israeli newspaper Haaretz reported that "several of them have died" in these detention facilities.

The report said the prisoners died at the Sde Teiman base near the city of Beersheva.

The detainees held at this facility are "blindfolded and handcuffed for most of the day and the lights are on at the facility throughout the night", the report said.

Concerns for the fate of detainees from Gaza heightened last week after Israeli television showed scores of stripped Palestinian men sitting on a Gaza street in military custody.

One clip showed the arm of a soldier in the foreground, suggesting it was filmed by a member of the military.

In another clip, a group of blindfolded men are seen sitting with their hands tied behind their backs as Israeli soldiers watch them.

Earlier this month the army announced that more than "500 terrorists" had been arrested in Gaza.

The war between Israel and Hamas, which rules the Gaza Strip, began after the Islamist group carried out a bloody attack on southern Israel on October 7 which killed around 1,140 people, according to an AFP tally based on the latest official Israeli figures.

Israeli's ensuing military campaign in Gaza has so far killed at least 20,000 people, the majority of them children and women, according to the Hamas government.