UN war crimes investigators have denounced a staggering loss of civilian life" caused by the US-backed campaign to reclaim Raqqa, the de facto capital of Islamic State. The independent commission of inquiry tasked with investigating violations of international law, war crimes and crimes against humanity in Syria said the intensification of airstrikes by the US-led coalition had led to the deaths of at least 300 civilians in the city. The Raqqa operation began last week with a ground assault by the Syrian Democratic Forces (SDF), an umbrella group comprising Kurdish and Arab militiamen armed by the US and supported by coalition airstrikes. "The intensification of airstrikes ... has resulted not only in staggering loss of civilian life, but has also led to 160,000 civilians fleeing their homes and becoming internally displaced," Paulo Pinheiro, the chairman of the UN commission of inquiry, told the human rights council in Geneva. The civilian cost of the campaign was highlighted last week when footage emerged of coalition planes deploying white phosphorus in the city, which is home to tens of thousands of civilians, prisoners of war, enslaved Yazidi women, and a few thousand Isis militants. Human Rights Watch urged the coalition separately on Wednesday to exercise great caution when using white phosphorus, saying it could cause "horrific and long-lasting harm" in crowded cities such as Raqqa.