Of 251 people taken hostage during the October 7 attack, 97 remain in Gaza.
Israeli Prime Minister Benjamin Netanyahu said on Monday that Hamas militants "executed" six hostages whose bodies were recovered from Gaza, shooting them "in the back of the head".
"These murderers executed six of our hostages, they shot them in the back of the head," he said during a press conference, rejecting the notion that Israel should respond with "concessions" in Gaza ceasefire talks.
The killing of the six hostages, announced by Israeli officials on Sunday, has spurred an outpouring of grief in Israel as well as anger at the government for not sealing a deal that would have secured the hostages' release.
Israel's health ministry said on Sunday that the six hostages were shot at close range shortly before their bodies were recovered from the Gaza Strip.
As thousands of protesters gathered in Tel Aviv on Monday for a second consecutive day of demonstrations criticising the government, Netanyahu sought forgiveness for not being able to save them but also appealed for unity.
He called on the international community to apply more pressure on Hamas to end the war triggered by the militants' unprecedented October 7 attack on southern Israel.
"We say yes, they say no all the time, but they also murdered these people and now we need maximum pressure on Hamas," he said.
"Hamas has to make the concessions."
Netanyahu also insisted on Monday that Israeli forces must retain control over the Philadelphi Corridor along the Egypt-Gaza border, which has emerged as a primary sticking point in talks mediated by the United States, Egypt and Qatar.
Hamas is demanding a complete Israeli withdrawal from the area as part of the stalled talks.
"The achievement of the war's objectives goes through the Philadelphi Corridor," Netanyahu said.
"Control of the Philadelphi axis guarantees that the hostages will not be smuggled out of Gaza," he added.
"I will not give in to pressure."
Of 251 people taken hostage during the October 7 attack, 97 remain in Gaza, including 33 the Israeli military says are dead.