Islamic State tunnels under al-Bab point to hard fighting ahead

FILE PHOTO: Rebel fighters inspect a tunnel they said belonged to Islamic State fighters which connects the city to Aqeel mountain, in the northern Syrian city of al-Bab, Syria March 13, 2017. REUTERS/Khalil Ashawi/File Photo

AL-BAB, Syria (Reuters) - Syrian rebels who drove Islamic State from the town of al-Bab in northwest Syria this year discovered an extensive network of tunnels dug by militants as part of their defences, a tactic that has slowed the military campaign against them.

"The tunnels complicated the fighting a lot and stopped our advance for weeks," said Mohammed Abu Yousef, a rebel in a group fighting under the banner of the Free Syrian Army as part of a Turkey-backed military campaign in north Syria.