Israel recovered the bodies of six hostages from a tunnel in southern Gaza where they were apparently killed not long before Israeli troops reached them, the military said on Sunday.

"According to our initial estimation, they were brutally murdered by Hamas terrorists a short time before we reached them," military spokesperson Rear Admiral Daniel Hagari told reporters in a briefing.

Days earlier, Qaid Farhan Alkadi, a member of the Bedouin community in southern Israel, was rescued about a kilometre away, the military said.

The Israeli military said the bodies of Carmel Gat, Hersh Goldberg-Polin, Eden Yerushalmi, Alexander Lobanov, Almog Sarusi and Ori Danino had been brought to Israel.

U.S. President Joe Biden, who has closely followed the fate of the hostages seized on Oct. 7, said the six included Israeli American Goldberg-Polin.

"I am devastated and outraged," Biden said in a statement issued by the White House.

After Alkadi was located, Israeli troops were told to be more cautious because of the likelihood that there might be other hostages in the area, but there had been no precise information on the location of the hostages, Hagari said.

Hamas and its armed wing did not immediately comment on the accusations.

At least 40,691 Palestinians have been killed and 94,060 injured in Israel's military offensive in the Gaza Strip since Oct. 7, the enclave's health ministry said in a statement on Saturday.

The war was triggered when Palestinian Islamist group Hamas attacked Israel, killing 1,200 and taking about 250 hostages, according to Israeli tallies.

On Saturday, clashes broke out between Israeli troops and Palestinian fighters in the occupied West Bank as Israel pushed ahead with a military operation in the flashpoint city of Jenin. Hundreds of Israeli troops have been carrying out raids since Wednesday in one of their largest actions in the West Bank in months.

Goldberg-Polin, captured at a music festival near Gaza, appeared in a video released by Hamas in late April.

"He had just turned 23. He planned to travel the world," Biden said. His parents, Rachel Goldberg and Jon Polin, "have been courageous, wise, and steadfast, even as they have endured the unimaginable," Biden said.

"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 said.

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, speaking to reporters in Rehoboth Beach, Delaware, Biden said he was "still optimistic," about a ceasefire deal to stop the conflict.

"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."