The report said it was "reasonable to assess" that Israel has used weapons in ways inconsistent with international humanitarian law but that the United States could not reach "conclusive findings."

The report had been held up for several days by debate within the State Department and was finally released after President Joe Biden publicly threatened to withhold certain bombs and artillery shells from Israel if it goes ahead with an assault on the packed city of Rafah.

The report does not affect that decision, with the White House reiterating on Friday that it was concerned about Israeli military action around Rafah, where some 1.4 million Palestinians have taken shelter.

Biden, responding to critics within his Democratic Party concerned by the toll on civilians in the Gaza war, had in February issued a memorandum known as NSM-20 that asked countries that receive US military aid to make "credible and reliable" assurances they are complying with human rights laws.

Israel -- which launched a war against Hamas after the militants staged the deadliest ever attack on the country on October 7 -- made assurances to the United States and "identified a number of processes for ensuring compliance that are embedded at all levels of their military decision-making," said the public version of the report, which was submitted to Congress.

"The nature of the conflict in Gaza makes it difficult to assess or reach conclusive findings on individual incidents," it said.

"Nevertheless, given Israel's significant reliance on U.S.-made defense articles, it is reasonable to assess that defense articles covered under NSM-20 have been used by Israeli security forces since October 7 in instances inconsistent with its IHL obligations or with established best practices for mitigating civilian harm," it said, referring to international humanitarian law.

The report also said that while the Israeli Defense Forces have "the knowledge, experience and tools" to minimize harm, "the results on the ground, including high levels of civilian casualties, raise substantial questions as to whether the IDF is using them effectively in all cases."

But despite some "serious concerns," the report said that all countries receiving US military aid had made assurances credible and reliable enough "to allow the provision of defense articles covered under NSM-20 to continue."

A US official described the report as a snapshot and said the State Department was still monitoring the use of weapons.

The other recipients of US military aid covered by the report were Colombia, Iraq, Kenya, Nigeria, Somalia and Ukraine.