When the ISIL shock troops set out to conquer a city in Syria or Iraq, their first move has been to avoid a battle by spreading terror — using videos that show them savaging civilians and beheading captured soldiers.

If psychological warfare fails, the self-styled “Army of the Caliphate” has developed its own form of maneuver warfare, using the fleet of four-wheel drive U.S. Humvees seized from Iraqi army bases to outflank foes and throw them into confusion.

The highly mobile force has embraced technology and public relations but also is skilled at database management. It uses satellite uplinks to communicate from the field, and members say its forces have deployed reconnaissance drones.

It’s been 12 weeks since ISIL (Islamic State in Iraq and the Levant) seized vast territories in Iraq to add to the territory it already controlled in Syria. It did not surprise the western-backed rebel Free Syrian Army.

Some outsiders have written them off as weak, uncoordinated and deeply factionalized, but the rebels have experience fighting ISIL since they ousted it from large parts of northern Syria early this year. What that experience has shown the rebels is that ISIL fighters are fierce and unafraid of death and a difficult match for an ill-equipped, disorganized rebel force.

In the past two months, moderate rebels have lost more ground to ISIL, particularly in eastern Syria. But rebel officers, most of them defectors from the Syrian army, say the Islamic extremists could be defeated with more international support and better internal organization.

At the same time, they warn that U.S. airstrikes, without ground spotters — a task they would like to fulfill — would be counterproductive and controversial, because ISIL, with no permanent bases, uses civilians as human shields.

But they say it would be a mistake to underestimate the determination of ISIL, whose ranks don suicide belts as they go into battle. “They are ready to die, willingly. They are not afraid of anything,” said Capt. Iyad Shamsi, who witnessed ISIL’s takeover of Abu Kamal, on the Syria-Iraq border.