An "unprecedented" new study released on Thursday revealed that the U.S.-led bombing campaign on Raqqa, Syria in 2017—which one military commander at the time claimed was the "most precise air campaign in history"—killed an estimated 1,600 innocent civilians while leveling the city on a scale unparalleled in recent decades.

The research collated almost two years of investigations into the assault on Raqqa, the groups said in a statement,  and "gives a brutally vivid account" of the enormous number of civilian lives lost as "a direct result" of thousands of coalition air strikes and tens of thousands of US artillery strikes in Raqqa from June to October 2017.

The report—"Rhetoric vs. Reality: How the 'Most Precise Air Campaign in History' Left Raqqa the Most Destroyed City in Modern Times"—is detailed on the interactive website created by investigative news organization Airwars and the human rights group Amnesty International-USA which carried out what they call the "most comprehensive investigation into civilian deaths in a modern conflict."