Gaza City, Gaza - The UN voiced concern as Israel Friday began sending back to war-ravaged Gaza thousands of Palestinian workers who had been present in Israel when the war began.

The workers may not have homes to return to and face grave dangers from ongoing military clashes in the territory, UN human rights office spokeswoman Elizabeth Throssell told a press conference in Geneva.

"I understand that among these people who are being sent back are those Palestinian workers and hospital patients who had been detained in the aftermath of October 7," Throssell said.

Gaza's health ministry says more than 9,000 people in the Palestinian enclave, mostly women and children, have been killed by the Israel bombing campaign in retaliation to the October 7 Hamas attack that killed 1,400.

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Before the war started, some 18,500 Gazans held Israeli work permits, according to COGAT, the Israeli defense body responsible for Palestinian civilian affairs.

"We were very concerned that at least 4,000 Palestinian workers and hospital patients were detained without sufficient legal basis in military facilities after Israel revoked their permits," Throssell said.

"There are worrying reports that some are being sent back into Gaza, despite the gravity of the situation there," Throssell said.

"We don't know exactly to where, it probably isn't clear whether they have got even a home to go to, and it's an incredibly difficult and dangerous situation."

AFPTV footage shot early Friday showed groups of workers – some of them visibly injured – arriving through the Karem Abu Salem crossing between Israel and southern Gaza, which is normally only used for goods.