Kurdish forces have carried out a wave of forced displacement and mass house demolitions - amounting to war crimes - in northern Syria, a rights group says. A report by Amnesty International accuses the Popular Protection Units (YPG) of razing entire villages after capturing them from Islamic State (IS). This appeared to be in retaliation for residents' perceived sympathies with or links to the jihadist group, it says. The YPG has consistently denied accusations of forced displacements However, the YPG - a key ally of the US-led international coalition against IS - and its political parent the PYD have admitted to some "isolated incidents". Coalition air strikes, as well as air drops of weapons and ammunition, have helped the militia to drive IS out of large parts of northern Syria this year. The Amnesty report came as the US said it had dropped more than 45 tons of ammunition to rebels in north-western Syria.