Just breaking, more details are likely going to be added to the article in the next hours:
http://www.bbc.com/news/world-middle-east-40271450
EDIT:
Article has been updated:
UN war crimes investigators say US-led coalition air strikes on Islamic State militants in the Syrian city of Raqqa are causing "staggering loss of life".
Coalition warplanes are supporting an offensive on the IS stronghold that was launched last week by an alliance of Kurdish and Arab fighters.
Since then, the Syrian Democratic Forces (SDF) have taken territory to the west, east and north of the city.
The battle has already led to 160,000 civilians fleeing their homes.
http://www.bbc.com/news/world-middle-east-40271450
EDIT:
Article has been updated:
"We note in particular that the intensification of air strikes, which have paved the ground for an SDF advance in Raqqa, has resulted not only in staggering loss of civilian life, but has also led to 160,000 civilians fleeing their homes and becoming internally displaced."
The UK-based monitoring group Airwars estimates that more than 600 civilians were killed in more than 150 coalition or SDF attacks between March and May.
Air and artillery strikes killed dozens more in the first eight days of June, it says.
The UN Office for the Co-ordination of Humanitarian Affairs warned on Thursday that the assault was intensifying an "already desperate" situation in Raqqa.
Air strikes, shelling and clashes on the ground were killing and injuring civilians, and damaging key infrastructure, it said. There were also reports of increased shortages of essential commodities such as food, medicine and fuel, it added.
Separately, Human Rights Watch warned that the coalition's use of artillery-delivered white phosphorus in Raqqa and in the last remaining IS-held parts of the northern Iraqi city of Mosul was endangering civilians.
White phosphorus can be used for several purposes on the battlefield - as a smoke screen, for signalling and marking, and as an incendiary weapon.
However, international law prohibits its use in civilian areas because of its indiscriminate effects. On contact, it can burn people, thermally and chemically, down to the bone.
"No matter how white phosphorus is used, it poses a high risk of horrific and long-lasting harm," warned Steve Goose, arms director at Human Rights Watch.