(Reuters) -- Amnesty International said on Tuesday tactics used by Iraqi forces and their U.S.-led coalition allies in the battle for Mosul violated international humanitarian law and might amount to war crimes.
The rights group said in a report the Islamic State militant group had also flagrantly violated humanitarian law by deliberately putting civilians in harm's way to shield their fighters and impede the advance of Iraqi and coalition forces.
Iraqi Prime Minister Haider al-Abadi declared victory in Mosul on Monday, three years after Islamic State seized the city and made it the stronghold of a "caliphate" the Sunni Islamist group said would take over the world.
A 100,000-strong alliance of Iraqi government units, Kurdish peshmerga fighters and Shi'ite militias launched the offensive to recapture the city in October, with air and ground support from the international coalition.
Much of Mosul has been destroyed in grinding street-to-street fighting. Thousands of civilians have been killed and nearly a million forced to flee their homes, according to the United Nations.
Amnesty said Iraqi forces and the coalition had carried out a series of unlawful attacks in west Mosul since January, relying heavily on Improvised Rocket Assisted Munitions (IRAMs), weapons with crude targeting capabilities that wreaked havoc in densely populated areas.
"Even in attacks that seem to have struck their intended military target, the use of unsuitable weapons or failure to take other necessary precautions resulted in needless loss of civilian lives and in some cases appears to have constituted disproportionate attacks," the report said.
Neither the Iraqi defense ministry nor coalition officials were immediately available to comment on the Amnesty report.
U.N. High Commissioner for Human Rights Zeid Ra'ad Al Hussein said in a statement on Tuesday there were allegations of rights abuses by Iraqi forces and by individuals taking revenge against captured Islamic State fighters or people accused of supporting them.
He called on the government in Baghdad to investigate the charges and hold those responsible to account.
Amnesty said that during the battle for Mosul, Islamic State fighters had rounded up residents and forced them to move into conflict zones for use as human shields.
As fighting neared, they trapped the civilians inside houses without access to food or medical care, it said.
Islamic State summarily killed hundreds, if not thousands, of men, women and children who attempted to flee and left the bodies of some hanging in public places, according to the report.
Amnesty acknowledged the difficulty of protecting civilians, but accused Iraqi authorities and the coalition of failing to take feasible precautions to protect them from air strikes. It said leaflet drops warning of attacks had been virtually useless because Islamic State heavily restricted civilian movement.
Neither the government nor the coalition keep track of civilian deaths. Amnesty said the toll just in west Mosul from attacks launched by pro-government forces was very likely higher than the 3,706 estimated by monitoring group Airwars.
"The true death toll of the west Mosul battle may never be known," it said.
Additional reporting by Stephanie Nebehay in Geneva; Editing by Andrew Roche.