The Islamic state stronghold is effectively encircled, under attack by Iraqi soldiers, Kurdish fighters and Shiite militias, advancing from all sides, and backed by US war planes.
Til now the offensive has focused on clearing the jihadists from surrounding villages. But this marks the first advance into the actual city. Mosul is by far the largest city held by Islamic State, and it's loss would mark their effective defeat in Iraq. But the battle is shaping up to be one of the bloodiest in a decade of turmoil.