Syrian military forces, trained and armed by the U.S., appear to have used white phosphorus in or near the Islamic State stronghold of Raqqa in recent days, causing concern for the wellbeing of civilians in the area.

On 8 June 2017, the citizen-journalist group Raqqa Is Being Slaughtered Silently posted a video on Twitter showing what looks like white phosphorus munitions exploding over what the group said was a Raqqa neighborhood:

The following day, the group posted a series of images:

Human Rights Watch is investigating the reports but appeared to confirm, in a statement, that the video did indeed show white phosphorus munitions. However, the group could not say whether the deployments have exposed civilians to any harmful effects.

We have not been able to determine much about the Raqqa [incident] since it’s unclear from the videos where exactly the white phosphorus impacted, given the way it was filmed.

International agreements, including the Geneva Conventions, ban the use of incendiary weapons like white phosphorus in civilian-populated areas, but it is not a violation of international law to deploy the substance to create a smokescreen in combat or to mark out targets for airstrikes.

White phosphorus can cause severe chemical burns on contact with skin as well as organ failure, with potentially fatal consequences.

Earlier in June, video posted by the Islamic State news agency Amaq appeared to show white phosphorus deployed in the Iraqi city of Mosul.

This is the longer version of Amaq video of White phosphorous used yesterday in Zanjili neighborhood of west Mosul #Iraq pic.twitter.com/9QTQhAlDSw — Fazel Hawramy (@FazelHawramy) June 4, 2017

In this video, the munitions appear to be bursting closer to the ground, in what could be an attempt to minimize their area of impact. White phosphorus burst at a higher altitude, as appears to be the case in the Raqqa video, spreads more widely, making its effects less precisely targeted.

The New York Times cited an unnamed U.S. official as confirming that American forces in Syria and Iraq do have access to white phosphorus, but the official insisted that it was not being deployed against civilians.

U.S. Army Colonel Ryan Dillon told the Washington Post that the U.S. military only uses white phosphorus in “accordance with the law of armed conflict” – for example “for screening, obscuring and marking in a way that fully considers the possible incidental effects on civilians and civilian structures.”

He added:

The coalition takes all reasonable precautions to minimize the risk of incidental injury to non-combatants and damage to civilian structures.

When we asked them for comment, the Combined Joint Task Force for Operation Inherent Resolve, which coordinates Coalition military operations against the Islamic State, made a similar statement:

As a matter of policy the Coalition does not discuss the employment of specific weapons and munition usage; n accordance with the law of armed conflict white phosphorus rounds are used for screening, obscuring, and marking in a way that fully considers the possible incidental effects on civilians and civilian structures. The Coalition takes all reasonable precautions to minimize the risk of incidental injury to non-combatants and damage to civilian structures. However, ISIS continues its blatant disregard for innocent human life by killing civilians trying to flee the fighting and the Coalition will not stand idly by and allow civilians to die needlessly if we can help protect them.

In October 2016, Amnesty International said it had received “credible witness and photographic evidence” that Iraqi and coalition forces had deployed white phosphorus near the Iraqi village of Karemlesh, which is 20 miles from the city of Mosul.

The human rights group warned that, because white phosphorus ignites on exposure to air, even buried munitions deployed in an area uninhabited by civilians could cause serious harm if civilians were to come across them at a later time.

Tarek Wheibi, Amnesty International’s Media Manager for the Middle-East and North Africa, told us in an email:

Amnesty International has not been able to independently verify the footage coming out of al-Raqqa. We are still investigating the reports and are deeply concerned for the safety of the thousands of civilians who remain trapped in and around the city.

He added: