Damaged buildings in the old city of Raqqa, August 19, 2017 (Zohra Bensemra/Reuters)

The US-led coalition, supporting the recapture of Syria’s Raqqa from the Islamic State in 2017, killed more than 1,600 civilians — 10 times the number acknowledged by the American military — according to Amnesty International and Airwars.

The organizations spent 18 months researching the deaths, including two months on the ground in Raqqa. They said the cases probably amounted to violations of international humanitarian law, calling for coalition members to compensate victims and their families.

The coalition responded that it takes “all reasonable measures to minimize civilian casualties”. Spokesman Scott Rawlinson said in an e-mail statement:

Any unintentional loss of life during the defeat of Daesh [Islamic State] is tragic.

However, it must be balanced against the risk of enabling Daesh to continue terrorist activities, causing pain and suffering to anyone they choose.

The Islamic State captured Raqqa in 2014 from Syrian rebels, proclaiming the city as the capital of its caliphate in the country.

In autumn 2015, the US created the Kurdish-led Syrian Democratic Forces to push the Islamic State out of northern and eastern Syria. Raqqa, the 7th-largest city in the country, was taken in October 2017 after a five-month offensive.

Amnesty documents incidents such as a September 25, 2017 airstrike that killed four families in the basement of a five-story building which was destroyed. The raid slew at least 32 civilians: four men, eight women and 20 children.

The investigation identified almost 500 “harm events” from Coalition operations. On four visits to Raqqa, Amnesty researchers investigated more than 200 strike locations and interviewed more than 400 witnesses and survivors.

The project identified when each of more than 11,000 destroyed buildings in Raqqa was hit, working with more than 3,000 digital activists in 124 countries.

Airwars researchers independently tracked 429 alleged civilian harm events during the battle for Raqqa.