It causes skin to melt away from the bone and can break down a victim's jawbone, but white phosphorus - known in Vietnam as Willie Pete - is still used by sections of the world's military.

There have been documented civilian casualties from the use of white phosphorus in war zones around the world, including Syria, Afghanistan, Gaza and elsewhere, according to Human Rights Watch.

US forces have used white phosphorus against enemy forces in 20th-century conflicts, including World War II and Vietnam.