By Howard Goller

(Reuters) -The Israeli military acknowledged on Monday that Palestinian civilians were harmed at aid distribution centres in the Gaza Strip, saying that new instructions had been issued to Israeli forces following "lessons learned".

Since Israel lifted an 11-week aid blockade on Gaza on May 19, allowing limited U.N. deliveries to resume, the United Nations says more than 400 Palestinians have been killed while seeking handouts of aid.

"Following incidents in which harm to civilians who arrived at distribution facilities was reported, thorough examinations were conducted in the Southern Command and instructions were issued to forces in the field following lessons learned," the Israeli military said in a statement.

It said incidents in which Gaza civilians were harmed were under review.

A senior U.N. official said on Sunday that the majority of people killed were trying to reach aid distribution sites of the U.S.-backed Gaza Humanitarian Foundation.

The GHF began distributing food packages in Gaza at the end of May, overseeing a new model of deliveries which the United Nations says is neither impartial nor neutral.

But many Gazans say they have to walk for hours to reach the sites, meaning they must start travelling well before dawn if they are to stand any chance of receiving food.

United Nations Secretary-General Antonio Guterres said on Friday that a U.S.-backed aid operation in Gaza is “inherently unsafe,” adding: “It is killing people.”

Israel and the United States want the U.N. to work through the GHF, but the U.N. has refused, questioning its neutrality and accusing the distribution model of militarising aid and forcing displacement.

"Any operation that channels desperate civilians into militarised zones is inherently unsafe. It is killing people, Guterres told reporters.  

Responding to Guterres on Friday, Israel’s Foreign Ministry said its military never targets civilians and accused the U.N. of “doing everything it can” to oppose the GHF aid operation.

“In doing so, the U.N. is aligning itself with Hamas, which is also trying to sabotage the GHF’s humanitarian operations,” it posted on X.

A GHF spokesperson said on Friday there had been no deaths at or near any of the GHF aid distribution sites. Israel and the United States have accused Hamas of stealing aid from the U.N.-led operations, which the Palestinian militants deny.

The war erupted after Hamas-led militants in Gaza took 251 hostages and killed 1,200 people, most of them civilians, in an October 7, 2023 attack, Israel's single deadliest day.

Israel's military campaign has since killed more than 56,000 Palestinians, most of them civilians, according to health authorities in Gaza, and flattened much of the coastal enclave.

(Reporting by Howard Goller, additional reporting by Hatem Maher; editing by Alex Richardson and Mark Heinrich)