During the offensive to reclaim the Syrian city of Raqqa from Islamic State rule, US, British and French coalition forces launched thousands of airstrikes and tens of thousands of artillery shells, hitting virtually every street.

We’ll perhaps never know how many civilians they killed. Coalition commanders insist on the precision of their airstrikes, but precision airstrikes are only as precise as the information about the targets. Then there’s the size of the bombs dropped. Time and again, we saw entire buildings destroyed in Raqqa. When bombs big enough to take out whole buildings are being used, as well as artillery with wide-area effects, any claims about minimising civilian casualties are unsupportable.

Coalition commanders emphasise the “incredible lengths” they said they went to in order to avoid civilian casualties. They beamed surveillance drone footage into a control room more than 1,200 miles away, they said, where sometimes they watched a building for 90 minutes before striking it.

But such surveillance apparently didn’t detect the thousands of civilians cowering in backrooms or basements, where they thought they had a chance of surviving. Not all those hiding were Isis fighters. In fact, many were also hiding from Isis. Residents told us they hid indoors and only went out to look for food and water. It’s what civilians the world over do when trapped in war. It’s what we would do, too.

Everyone we spoke to in Raqqa agreed that Isis had to be defeated. But they asked why their families had to be killed and their city destroyed in the process. The coalition remains stubbornly wedded to the notion that precision airstrikes allowed it to defeat Isis with a minimal cost to civilian life. This is wishful thinking, as Amnesty’s research has revealed in Raqqa (and before that in the Iraqi city of Mosul).

Coalition commanders have previously dismissed our findings out of hand, saying we have “no understanding of the brutality of warfare”. They are wrong. We do.

In Raqqa we visited dozens of sites and worked with military experts to examine patterns of destruction. We compared material evidence with the testimonies of survivors and witnesses we interviewed. The coalition could and should have done this too.

Minimising harm to civilians is not just good practice, it’s the law. Site visits and interviews with survivors and witnesses are a crucial part of any investigation. Without proper investigations, complying with the laws of war is all but impossible. In Raqqa, we didn’t meet a single survivor or relative of victims who had been interviewed or even contacted by the coalition, nor anyone who was aware of any visits by US, British or French officials to sites of strikes that killed civilians.

Amnesty is urging coalition members to impartially and thoroughly investigate incidents where civilian casualties are alleged to have occurred, and to publicly acknowledge the scale and gravity of the loss of civilian lives and destruction of civilian property in Raqqa.

Anything less denies victims justice and reparation, and risks repeating the same mistakes elsewhere.

• Donatella Rovera is Amnesty International’s senior crisis response adviser. Benjamin Walsby is a Middle East researcher for Amnesty