The eight Palestinians, some of them children, were killed in an explosion on a beach in the northern Gaza Strip on Friday. Many more people were wounded.
Initial reports said the deaths and injuries were caused by an Israeli shell. The military had been shelling the surrounding area from where Palestinian fighters have fired rockets into Israel.
But an internal inquiry by the military will say that the deaths were likely to have been caused by a mine placed at the beach.
Newspaper reports said that the inquiry would suggest that supporters of Hamas had been planting mines to prevent operations by Israeli special forces.
The commission "will apparently not determine the direct cause of the tragedy, but will mention that chances the blast was caused by ... artillery shell are slim", the Yediot Aharonot daily said.
The newspaper said the inquiry had found that shrapnel extracted from several of the injured did not match Israeli shells, and photos and television images of the crater produced by the explosion resembled that of a bomb or a mine.
It also said that Israeli intelligence had information that Hamas had been mining sections of the beach in recent days.
An army spokesman speaking to AFP said: "We have proceeded with detailed tests to get at the truth and it is clear that the certainty of responsibility by the Israeli army in this tragedy is diminishing more and more and that of the Palestinians increases."
Haaretz, another daily, carries a similar report, but also says: "The importance of the committee's findings are obviously mitigated by the fact that ultimately, the IDF is being cleared by an IDF investigation."
The military investigation was led by General Meir Klifi and is due to present its report to General Dan Halutz, chief of staff, on Tuesday evening.