US-led forces in Syria have been accused of dropping white phosphorous on districts in eastern Raqqa, as it battles to liberate the city from the Islamic State.

Video footage released by Amaq, the news agency run by Islamic State in Iraq and the Levant (Isil), appears to show the deadly substance falling on the Syrian capital on two separate occasions.

Raqqa is Being Saughtered Silently, an anti-Isil campaign group, has also released similar images on social media.

The use of white phosphorous in densely populated areas is banned under international law, though military forces are allowed to use it to create smoke screens.

Similar to napalm, white phosphorus causes agonising and potentially deadly chemical burns which have been known to melt skin off the bone.