MOSUL, Iraq — Yousef Ali peered through the scope of his Russian-made Dragunov sniper rifle. Through the small hole in the wall of an abandoned hotel, Ali saw the labyrinth of the Old City's narrow streets stretch before him.

Less than 300 yards away, the Islamic State, also known as ISIS, prepared for another sneak attack, surrounded by civilian human shields. "The (ISIS fighters) are out there," said the 20-year-old Iraqi federal policeman, taking his eyes off the scope for a moment. "Just behind those buildings."

The police forces have had an important role to play since the start an offensive in October to drive the militants from Mosul, their last major stronghold in Iraq. For the past few months, they've gained a higher profile taking out ISIS positions in western Mosul while creating escape routes for trapped civilians in tight quarters.

The federal police, including their elite SWAT unit called the Emergency Response Division, are the Iraqi forces closest to the Old City. The police and SWAT unit will likely be the first to take the al-Nuri mosque, also known as the Great Mosque, whose capture would spell a symbolic victory over the Islamic State. It was there the head of the militant group declared a "caliphate" in Iraq and Syria after invading in 2014.

Federal police, many of them young and inexperienced, have taken the brunt of the casualties during the latest offensive.