Intensive US-led coalition bombardment on the Syrian city of Raqa killed more than 1,600 civilians over four months in 2017, according to a report released on Thursday.
The findings were compiled after months of field research and extensive data analysis, including via a project that saw 3,000 digital activists scan satellite imagery online.
In mid-2017, Raqa had been the de facto Syria capital of the Islamic State group's cross-border "caliphate" for three years and the US-led coalition launched a military campaign to crush the jihadists in their main remaining hub.
The unprecedented investigation, carried out by Amnesty International and the Airwars monitoring group, urged top coalition members to show more transparency and accountability.
"Many of the air bombardments were inaccurate and tens of thousands of artillery strikes were indiscriminate," said Donatella Rovera, crisis response advisor at Amnesty.
The civilian death toll for the coalition campaign, which supported Kurdish-led ground forces in their successful advance against IS, stands at more than 1,600, according to the report.
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The coalition has admitted to around 10 percent of those deaths, it said.
"Coalition forces razed Raqa, but they cannot erase the truth," Rovera said.
"Amnesty International and Airwars call upon the Coalition forces to end their denial about the shocking scale of civilian deaths and destruction caused by their offensive in Raqa."