GAZA/JERUSALEM - New instructions have been issued to the fighters charged with guarding the prisoners regarding how to deal with them if the Israeli army approaches the detention site, Hamas said on Monday.

Israeli Prime Minister Benjamin Netanyahu and the Israeli army alone "bear full responsibility for the deaths of prisoners after they deliberately obstructed any prisoner exchange deal for narrow interests, in addition to their deliberate killing of dozens of them through direct aerial bombardment," Abu Obeida, the spokesman for the Al-Qassam Brigades, the military wing of Hamas, said in a statement.

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"Netanyahu's insistence on releasing the prisoners under military pressure instead of closing a deal will result in them returning to their families in coffins and their families having to choose whether they are dead or alive," Abu Obeida added.

The statement came after the Israel Defense Forces (IDF) said six bodies, including two women and four men, were discovered on Saturday in an underground tunnel in the Rafah area, southern Gaza.

All six were taken hostage during Hamas' surprise attack on Oct 7, 2023, which left around 1,200 people dead and approximately 250 others captured.

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According to an initial assessment by the IDF, the hostages were estimated to be brutally murdered by Hamas terrorists 48-72 hours before the Israeli troops reached them.

Netanyahu on Monday vowed that Hamas will "pay a heavy price".

"Israel will not ignore this massacre. Hamas will pay a very heavy price for this," Netanyahu said in a news conference, adding that the price will be exacted "in the short term".

Meanwhile, Hamas confirmed in a press statement that the bodies were found by the Israeli army in a tunnel in Rafah but noted that they "were killed by Israeli shelling".

Hundreds of thousands of Israelis rallied across Israel on Sunday and Monday, demanding Netanyahu negotiate a ceasefire with Hamas to secure the return of hostages held in Gaza.

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In Monday's news conference, Netanyahu also said Israel is "not going to withdraw from the Philadelphi Corridor."

"We need to have it under our control," which is critical for preventing future weapons smuggling from Egypt to Gaza, he said, calling for unity within his cabinet concerning the matter.

The Israeli army took control of the Philadelphi Corridor, a 100-meter wide and 14-km-long buffer zone along the Egypt-Gaza border, and the Palestinian side of the Rafah crossing in May, which halted the entry of humanitarian aid trucks from Egypt into Gaza.