Weapons supplied by Britain, the US, European nations and Iran have been used by Shia militias in Iraq accused of committing war crimes against local Sunni populations.

A report by the human rights group Amnesty International has detailed how paramilitary organisations nominally operating as part of the Iraqi armed forces in the fight against the Islamic State (Isis/Daesh) are using arms from Iraqi military stockpiles, provided by the US, Britain and Europe, Russia and Iran, to commit war crimes, revenge attacks and other atrocities.

Research and analysis of photographic and video evidence since June 2014 has found that these paramilitary militias have benefited from transfers of arms manufactured in at least 16 countries, which include tanks and artillery as well as a wide range of small arms.

During the fightback against the IS, international NGOs have said the predominantly Shia militias have used those arms to facilitate the enforced disappearance and abduction of thousands of mainly Sunni men and boys, torture and extrajudicial executions as well as destruction of property.

Amnesty International has focused on four main militias from the 40 or 50 distinct militias which were established in mid-2014 to aid in the fight against IS saying the Badr Brigades, Asa'ib Ahlal-Haq, Hezbollah and the Saraya al-Salam Brigade have committed serious human rights violations.

"The Iraqi authorities have helped to arm and equip the [militias] and pay their salaries – they must stop turning a blind eye to this systematic pattern of serious human rights violations and war crimes," Patrick Wilcken, Researcher on Arms Control and Human Rights at Amnesty International, said in a statement.

"International arms suppliers, including the USA, European countries, Russia and Iran, must wake up to the fact that all arms transfers to Iraq carry a real risk of ending up in the hands of militia groups with long histories of human rights violations," he added.