Even with major powers such as the United States, Russia, France and United Kingdom conducting relentless airstrikes on Islamic State (ISIS) targets in Syria, the question remains: How can this terrorist group be completely crushed?

A retired officer of the U.S. Army Special Forces, otherwise known as the "Green Berets," is suggesting a community approach to the fight against ISIS, as well as tighter American policies on immigrants.

In an interview with WND.com, retired U.S. Army Lt. Col. Scott Mann, who served the U.S. military for 23 years, said the campaign against ISIS should start with completely understanding how the jihadist group operates.

"They go into areas that are beyond the reach of a fragile government and co-opt and manipulate tribes and clans at a community level," the retired Army officer explained to WND.com. "That's how they set up their shop."

Keeping this in mind, the U.S. government should then try a community approach in defeating the ISIS, which involves local Sunni tribes in Syria leading the military effort.

"If you're not willing to work in these dark and tough areas where ISIS and al-Qaeda set up shop, then you shouldn't even do this kind of programme," Mann said.

"That's exactly what we did in Syria. We basically brought in and recruited marginally vetted groups. We trained them behind the fortification of where our troops were. Then we basically launched them out and said, 'Have a nice time storming the castle,'" he added, in an apparent swipe at the failed U.S. efforts to train Syrian rebels against the ISIS.

Mann further said that battling the ISIS on the ground will not be enough. The terrorist group, he said, should also be crushed in cyberspace, where ISIS militants spread their organisation's extremist propaganda.

The retired Army officer also suggested that the US should tighten its immigration policies.

"For starters, how about securing the southern border? For starters, how about just an honest look at our immigration and our visa policy as it currently stands in relation to what terrorists are exploiting now?" Mann said.