The bodies of Carmel Gat, Eden Yerushalmi, Hersh Goldberg-Polin, Alexander Lobanov, Almog Sarusi, and Master Sergeant Ori Danino were found and recovered on Saturday.

"Goldberg-Polin had just turned 23. He planned to travel the world," Biden was quoted as saying by Reuters.

His parents, Rachel Goldberg and Jon Polin, "have been courageous, wise, and steadfast, even as they have endured the unimaginable," he said, stated the report.

Goldberg-Polin, who was taken hostage at a music festival near Gaza, was seen in a video released by Hamas in late April.

"They have been relentless and irrepressible champions of their son and of all the hostages held in unconscionable conditions. I admire them and grieve with them more deeply than words can express," the president was quoted as saying by Reuters.

Biden vowed that "Hamas leaders will pay for these crimes. And we will keep working around the clock for a deal to secure the release of the remaining hostages."

Vice President Kamala Harris said in a statement, "I strongly condemn Hamas’ continued brutality, and so must the entire world." Harris, the Democratic candidate running to succeed Biden, said she and he would never waver in their commitment to free the Americans and all those held hostage in Gaza.

Earlier, in Delaware’s Rehoboth Beach, Biden said he was "still optimistic" about a ceasefire deal to stop the prolonged conflict, Reuters reported.

"I think we're on the verge of having an agreement," he said. "It's time this war ended."

Biden added that "people are continuing to meet."

"We think we can close the deal, they’ve all said they agree on the principles."

According to Reuters, Israel’s President Isaac Herzog said, "The heart of an entire nation is shattered to pieces.

"I embrace their families with all my heart, and apologize for failing to bring them home safely."

Prime Minister Benjamin Netanyahu did not release a statement immediately over the brutal killing of the hostages.

According to the report, Netanyahu is under pressure to reach a ceasefire agreement with Hamas that includes the release of remaining hostages.

Senior Hamas official Izzat El-Reshiq said that Israel, in its refusal to sign a ceasefire deal, was responsible for the deaths.

According to Israel's Hagari, hostage Qaid Farhan Alkadi from the Bedouin community in southern Israel, was rescued days earlier, about a kilometre away.

The six recovered bodies were among the 250 hostages taken during Hamas' attack on southern Israel on October 7, which triggered the ongoing war in Gaza.

The assault resulted in around 1,200 deaths, according to Israeli reports.

Since then, the health ministry in Gaza has reported at least 40,691 Palestinians killed and 94,060 injured in Israel's military counter-attack.

Sunday's developments are likely to intensify protests by Israelis demanding a deal for the hostages' release.

The Hostage Families Forum has called on Netanyahu to take responsibility and clarify what is delaying an agreement.