Israeli authorities have caused a forced displacement of Palestinian people in Gaza to an extent that constitutes war crimes and crimes against humanity, Human Rights Watch said in a report on Thursday.

The report is the latest in a series from aid groups and international bodies warning about the dire humanitarian situation in the besieged enclave.

"Human Rights Watch found that forced displacement has been widespread, and the evidence shows it has been systematic and part of a state policy. Such acts also constitute crimes against humanity," the report said.

There was no immediate comment from the Israeli military or foreign ministry, but Israeli authorities have previously rejected such accusations and say their forces operate in compliance with international law.

The law of armed conflict forbids the forcible displacement of civilian populations from occupied territory, unless necessary for the security of civilians or imperative military reasons.

Israel invaded the Gaza Strip last year after Hamas-led gunmen attacked communities in southern Israel, killing around 1,200 people, according to Israeli authorities, and abducting more than 250 as hostages.

Since then, the Israeli campaign has killed more than 43,500 people, according to Gaza health authorities, and destroyed much of the enclave's infrastructure, forcing most of the 2.3 million population to move several times.

For the past month, Israeli troops have moved tens of thousands of people from areas in the north of the enclave as they have sought to destroy Hamas forces the military says have been reforming around the towns of Jabalia, Beit Lahiya and Beit Hanoun.

Human Rights Watch said the displacement of Palestinians "is likely planned to be permanent in the buffer zones and security corridors," an action it said would amount to "ethnic cleansing."

The Israeli military has denied seeking to create permanent buffer zones and Foreign Minister Gideon Saar said on Monday that Palestinians displaced from their homes in northern Gaza would be allowed to return at the end of the war.