Columns of Iraqi and Kurdish forces backed by US-led air strikes started the slow advance towards Mosul, launching a long-awaited operation to retake Iraq's second largest city from the Islamic State group. The operation is expected to take weeks, even months. Once in Mosul, troops will have to fight their way into an urban environment where more than one million people still live. RT LIVE http://rt.com/on-air Subscribe to RT! http://www.youtube.com/subscription_center?add_user=RussiaToday Like us on Facebook http://www.facebook.com/RTnews Follow us on Twitter http://twitter.com/RT_com Follow us on Instagram http://instagram.com/rt Follow us on Google+ http://plus.google.com/+RT Listen to us on Soundcloud: https://soundcloud.com/rttv RT (Russia Today) is a global news network broadcasting from Moscow and Washington studios. RT is the first news channel to break the 1 billion YouTube views benchmark.