A group of soldiers who took part in Israel's assault in Gaza say widespread abuses were committed against civilians under "permissive" rules of engagement.
The troops said they had been urged to fire on any building or person that seemed suspicious and said Palestinians were sometimes used as human shields.
Breaking the Silence, a campaign group made up of Israeli soldiers, gathered anonymous accounts from 26 soldiers.
Israel denies breaking the laws of war and dismissed the report as hearsay.
The report says testimonies show "the massive and unprecedented blow to the infrastructure and civilians" was a result of Israeli military policy, articulated by the rules of engagement, and encouraged by a belief "the reality of war requires them to shoot and not to ask questions".
One soldier is quoted saying: "The soldiers were made to understand that their lives were the most important, and that there was no way our soldiers would get killed for the sake of leaving civilians the benefit of the doubt."
Until now, Israel always had a ready answer to allegations of war crimes in Gaza. Claims were, they said, Palestinian propaganda. Now the accusations of abuse are being made by Israeli soldiers.
The common thread in the testimonies is that orders were given to prevent Israeli casualties whatever the cost in Palestinian lives.
The Israeli military says past allegations of wrong-doing in Gaza were the result of soldiers recycling rumours.
But Breaking the Silence has a long - and to many, credible - record in getting soldiers to talk about experiences which might not reflect well on the army.
Breaking silence on abuses
Another says: "People were not instructed to shoot at everyone they see, but they were told that from a certain distance when they approach a house, no matter who it is - even an old woman - take them down."
Many of the testimonies are in line with claims made by human rights organisations that Israeli military action in Gaza was indiscriminate and disproportionate.
Amnesty International has accused both Israel and Hamas, the Palestinian militant group in charge in Gaza, of committing war crimes during the 22-day conflict which ended on 18 January.
Israeli officials insist troops went to great lengths to protect civilians, that Hamas endangered non-combatants by firing from civilian areas and that homes and buildings were destroyed only when there was a specific military need to do so.
'Ill discipline'
Other allegations in the testimonies of the 14 conscripts and 12 reserve soldiers include:
• Civilians were used as human shields, entering buildings ahead of soldiers
• Large swathes of homes and buildings were demolished as a precaution or to secure clear lines of fire for the future.
• Some of the troops had a generally aggressive, ill-disciplined attitude
• There was incidents of vandalism of property of Palestinians
• Soldiers fired at water tanks because they were bored, at a time of severe water shortages for Gazans
• White phosphorus was used in civilian areas in a way some soldiers saw as gratuitous and reckless
• Many of the soldiers said there had been very little direct engagement with Palestinian militants.
The report says Israeli troops and the people who justify their actions are "slid[ing] together down the moral slippery slope".
Israel spokeswoman disputes allegations
"This is an urgent call to Israeli society and its leaders to sober up and investigate anew the results of our actions," Breaking the Silence says.
Israel said the purpose of Operation Cast Lead had been to end rocket fire from Gaza aimed at its southern towns.
Palestinian rights groups say about 1,400 Palestinians died during the operation. Thirteen Israelis died in the conflict, including 10 soldiers serving in Gaza.
According to the UN, the campaign damaged or destroyed more than 50,000 homes, 800 industrial properties, 200 schools, 39 mosques and two churches.
Investigations
Reacting to the report, Israeli military spokeswoman Lt Col Avital Leibovich said:
"The IDF [Israel Defence Forces] regrets the fact that another human rights organisation has come out with a report based on anonymous and general testimony - without investigating their credibility."
She dismissed the document as "hearsay and word of mouth".
"The IDF expects every soldier to turn to the appropriate authorities with any allegation," Lt Col Leibovich added. "This is even more important where the harm is to non-combatants. The IDF has uncompromising ethical values which continue to guide us in every mission."
There have been several investigations into the conduct of Israel's operation in Gaza, and both Israel and Hamas, the Palestinian militant group that runs the territory, have faced accusations of war crimes.
An internal investigations by the Israeli military said troops fought lawfully, although errors did take place, such as the deaths of 21 people in a house that had been wrongly targeted.
A fact-finding team commissioned by the Arab League concluded there was enough evidence to prosecute the Israeli military for war crimes and crimes against humanity, and that "the Israeli political leadership was also responsible for such crimes".
It also said Palestinian militants were guilty of war crimes in their use of indiscriminate rocket attacks on civilians.
Front Page Features