Airstrikes against the de facto capital of the Islamic State terror group in northern Syria killed 40 civilians on Sunday, a monitor group reported.At least eight children were among those killed in the airstrikes against the northern city of Raqqa over the past 24 hours, said the Syrian Observatory for Human Rights.The London-based watchdog group said it was not immediately known whether the air raids were carried out by the Russians or Syrians.Raqqa in northern Syria has been self-declared by the IS as the capital of what they call the "caliphate". US-led air raids and Russian as well as Syrian warplanes usually strike IS positions in the city.