e battle to retake Mosul was always going to be hard, bloody, and long. But for many of the troops on the ground who've been fighting inside the city for the last ten days, it's rapidly becoming a nightmare, as they face wave after wave of Islamic State suicide bombers and snipers.
I'm Reuters' correspondent Dominic Evans in Baghdad.
the early stage of the campaign, the troops made rapid progress through the villages and towns outside the city. Now, they're fighting inside Mosul itself. It's an enormous city, it's far larger than any other they've been attacking in the last two years.
So, as well as the well trained specialist counter terrorism units, they've had to bring in other groups, other divisions, that are less well prepared for urban warfare. Including tank divisions, who can't use their tanks inside the built up narrow streets of Mosul. Islamic State have had two years to prepare their defense.
They've dug a network of tunnels across the city, which means they can spring up and surprise the troops at any stage. They can also blend in with the civilian population which is still living in Mosul.
top of that, they've got very well-honed trained tactics that they're using now.
They attack in waves. They give the army no respite, no rest. It's debilitating for the attacking forces. The overwhelming number of the attacking forces does make it very hard to imagine that Islamic State can hold out forever against this campaign. But the tactics they've used, the training, and the fierce determination make clear it's going to be a long and very hard fought war.