Daesh seized the northern Iraqi city of 2.5 million in June 2014. Mosul has since become the de facto Iraqi capital of the terrorist group.
Daesh, which is outlawed in Russia and many other countries, controls large swaths of land in oil-rich Syria, Iraq and Libya. It earns millions of dollars selling smuggled crude on the black market, according to Russian and US estimates.
The US-led coalition of 65 nations has been carrying out airstrikes against Daesh in Iraq since August 2014 and in Syria since September 2014 without the approval of the Syrian government or the UN Security Council.