Israel's account of its conduct during the Gaza war was challenged on Monday after evidence emerged apparently contradicting one of the army's key findings, The Guardian reported.

Israel last week submitted a 46-page response to a highly critical United Nations inquiry by South African judge Richard Goldstone, which accused both Israel and Hamas of "grave breaches" of the fourth Geneva Convention.

In the report, Israel claimed its forces abided by international law throughout the war last year and denied targeting the al-Badr flour mill in northern Gaza, which was severely damaged during the IDF's three-week offensive.

But the UN mine action team, which handles ordnance disposal in Gaza, maintains that the remains of a 500-pound Mk82 aircraft-dropped bomb were found in the ruins of the mill last January.

This evidence directly contradicts the Israeli report, which challenged allegations that the building was deliberately targeted and specifically stated there was no evidence of an air strike, The Guardian said.

Goldstone used the account of the air strike as a sign that Israel's attack on the mill was not mere collateral damage, but precisely targeted and a possible war crime.

Although no one died in the attack on what was the only operational mill in Gaza, the incident received particular criticism from Goldstone, who concluded that the bombing was "intentional and precise" and was "carried out for the purpose of denying sustenance to the civilian population".

He added that the attacks violated the fourth Geneva Convention and customary international law, and may constitute a war crime.

The Israeli report admitted the building had been hit by tank shells but said it was a "legitimate military target" because there were Hamas fighters "in the vicinity of the flour mill". It said the mill was "not a pre-planned target" and specifically denied it was hit by an air strike.

"The military advocate general did not find any evidence to support the assertion that the mill was attacked from the air using precise munitions, as alleged in the human rights council fact-finding report," it said. The military advocate general "found no reason" to order a criminal investigation.

But the Guardian claims to have visited the mill days after the war last year, finding on the first floor of the building what appeared to be the remains of an aircraft-dropped bomb.

The UN mine action team said it identified an aircraft-dropped bomb at the mill on 25 January last year and removed it on 11 February. "Item located was the front half of a Mk82 aircraft bomb with 273M fuse," the team reported.

"The remains of the bomb were found on an upper floor in a narrow walkway between burnt-out machinery and an outside wall." The bomb was made safe by a technical field manager and removed.