"As a result, we unfortunately expect an increase in mass casualty attacks and sabotage of economic infrastructure."
IS's territorial losses are not diminishing concerns about its intent and ability to strike abroad
The militants seized Falluja in January 2014, six months before they declared a "caliphate" over part of Syria and Iraq
Islamic State has begun allowing thousands of civilians trapped in central Falluja to escape
Clashes involving aerial bombardment, artillery and machine gun fire are continuing.
Falluja would be the third major city in Iraq recaptured by the government after Tikrit and Ramadi
The offensive appears to be the biggest Damascus has mounted against Islamic State since it recaptured the city of Palmyra
Tens of thousands of civilians are trapped in the city with limited access to water, food and healthcare.