U.N. Secretary-General Antonio Guterres called on Monday for an independent investigation into the deaths of at least 31 Palestinians near a U.S.-backed aid distribution site in Gaza, after rescuers blamed the deaths on Israeli gunfire.

"I am appalled by the reports of Palestinians killed and injured while seeking aid in Gaza yesterday. It is unacceptable that Palestinians are risking their lives for food," Guterres said in a statement. "I call for an immediate and independent investigation into these events and for perpetrators to be held accountable."

Climate campaigner Greta Thunberg and other 11 activists set sail on Sunday afternoon for Gaza on a ship aimed at "breaking Israel's siege" of the devastated territory, organizers said.

The sailing boat Madleen, operated by activist group Freedom Flotilla Coalition, departed from the Sicilian port of Catania, in southern Italy.

Kurdish security forces in northeast Syria said an Islamic State group attack killed three personnel on Sunday, as the jihadists keep up their attacks in Kurdish-controlled areas of the war-torn country.

Noting "escalating activity" by the jihadists, a statement from the Asayish security forces said an IS cell "targeted a patrol" from the force's convoy and road security department on the Raqa-Hasakeh road.

Gaza's civil defense agency said Israeli fire killed at least 22 people on Sunday near a U.S.-backed aid distribution center in the southern city of Rafah, revising an earlier death toll.

Hamas announced that it has replied to a U.S.-backed Gaza ceasefire proposal, but Washington's main negotiator criticized the response as "totally unacceptable".

Prince Faisal bin Farhan will become the first Saudi foreign minister to visit the occupied West Bank on Sunday, a diplomatic source told AFP, as the Gaza war drags on and Riyadh pushes for Palestinian statehood.

Israel struck western Syria overnight, the Israeli military and Syrian state media said, with one civilian reportedly killed in the first such attack on the country in nearly a month.

Israel has said that Hamas must accept a hostage deal in Gaza or "be annihilated", as U.S. President Donald Trump announced that a ceasefire agreement is "very close".

Defense Minister Israel Katz vowed on Friday to build a "Jewish Israeli state" in the occupied West Bank, a day after the government announced the creation of 22 new settlements in the Palestinian territory.

He said the move was a "clear message" to French President Emmanuel Macron, whom Israel's foreign ministry accused of carrying out a "crusade against the Jewish state."

Israeli airstrikes killed at least 14 people in the Gaza Strip, hospital officials said Friday, while Hamas was reviewing a new Israeli-approved ceasefire proposal after giving it an initial cool response.

President Donald Trump's Mideast envoy had expressed optimism this week about brokering an agreement that could halt the Israel-Hamas war, allow more aid into Gaza, and return more of the 58 hostages still held by Hamas, around a third of whom are alive.