HRW criticises US for using 'civilian-endangering' white phosphorous against IS in Syria and Iraq

Human Rights Watch says the US-led coalition fighting Islamic State in Syria and Iraq is endangering civilians by using artillery-delivered white phosphorous.

Steve Goose, the arms director for the New-York-based rights group, says in a statement Wednesday that "no matter how white phosphorus" is used, it poses "a high risk of horrific and long-lasting harm" in crowded cities like Raqqa and Mosul.

HRW, citing research and media reports, refers to several incidents in Raqqa and Mosul where artillery-fired white phosphorous was used but could not determine if there were casualties.

The group says the rationale for the use of the weapon is unclear as the US-led coalition doesn't comment on specific incidents.

US-led coalition warplanes allegedly used white phosphorus munitions as recently as last week in the Islamic State group's Syrian bastion of Raqqa, endangering the lives of civilians, local activists said.

White phosphorous is designed to illuminate battlefields at night, but can cause severe and lasting burns.

Raqqa 'showered with phosphorous'

Suspected US aircraft reportedly dropped the incendiary substance, which if used in the vicinity of civilian concentrations can be considered a war crime, over the city on Thursday, the activist-run Raqqa Is Being Slaughtered Silently claimed.

"In the name of fighting IS, the US-backed international coalition is dropping white phosphorous all across East and West Raqqa," the media collective said.

"White phosphorous is an incendiary weapon which can melt the flesh off a human to the bone," it added.

White phosphorus burns at extremely high temperatures upon exposure to air, posing a deadly risk to civilians.

The US government denies using the substance illegally, but admits its use to cover troop movements.

The US-led coalition against IS has recently upped the intensity of air raids on Raqqa, as US-backed Syrian fighters battle to take back the city.

An estimated 300,000 civilians were believed to have been living under IS rule in Raqqa, including 80,000 displaced from other parts of Syria.

But thousands have fled in recent months, and the UN humanitarian office estimates about 160,000 people remain in the city.