Take a look inside ISIS' newly-discovered escape tunnels outside of its Iraqi stronghold

Iraq Counter Terrorism Service forces have discovered several underground tunnels used by ISIS to escape Mosul on Thursday.

The forces have launched a campaign last week to retake the ISIS stronghold of Mosul, which, if successful, could "mark the beginning of the end" for the terrorist group.

ISIS is fighting back - sending hundreds of fighters to Mosul and preparing for fierce battles with intense defenses, according to CNN - while at the same time, the militant group has established an elaborate network of tunnels across the city and neighboring villages that are used as escape routes.

Here are some astonishing photos of ISIS' secret tunnels.