Human Rights Watch said the Israeli restrictions cast doubt on the government's claims that it is conducting its own investigations and there is no need for the ICC to get involved.
The report said Israel maintained that its investigations were in accordance with global standards despite the investigators not entering the strip.
Palestinian authorities are not known to have investigated any alleged serious crimes committed in or from Gaza, such as the firing of rockets by militant groups in Gaza toward Israeli civilian areas. HRW has also denounced Egypt for closing the Rafah security checkpoint and Hamas for preventing people from entering or leaving for a week.
Israel has repeatedly accused human rights groups like the HRW of being biased against it and even refused to grant a work permit to a regional director of the nonprofit, the Associated Pressreported.
Israel allowed the first ever visit in the country by the ICC in September 2016, but it had said the court had no authority to assess claims of war crimes against Palestinians.
The statement made no mention of Human Rights Watch or Amnesty.
Hamas has fought three wars with Israel since 2008.
"We coordinate the crossing of many human rights organizations", it said, naming the group "Doctors Without Borders" as an example. Hamas has accused Israel of the killing, and said it sealed its borders to catch those involved. "Israeli intelligence officers came to our house many times and gave us messages that Mazen would be liquidated if he continued with his actions", the report quoted him as saying. Until then, the authorities should add human rights workers to those eligible for travel permits. Travel restrictions on human rights workers, it said, were "unavoidable... due to weighty security and political considerations".