The 19-year-old flees the militants' last bastion in eastern Syria
Recovery operations were expected to last several days 'due to the huge area of the two mass graves'
SDF said over 3,000 civilians had left as part of a deal negotiated between Raqa Civil Council and Syrian IS fighters
Extremist group last week lost its key Syrian stronghold of Raqa
The declaration comes four days after US-backed Kurdish-led forces recaptured the Syrian city
Over 100 IS fighters had surrendered in Raqa over the past 24 hours, coalition says
IS reportedly withdrew from at least five key neighbourhoods
21 children among at least 59 civilians killed in the air strikes
The coalition estimates that around 2,500 besieged militants are defending the city
The battle for Raqa is the SDF's flagship offensive, with heavy backing from coalition air strikes and weapons