Officials said Al Qaida has developed methods to rapidly take control of Sunni neighborhoods and cities in Iraq, Middle East Newsline reported. They said Islamic operatives employ intimidation, bribes and indoctrination.

"They don't generally have, actually, a high degree of support from the population," David Kilcullen, a senior U.S. counter-insurgency adviser, said.

"The very fabric of Iraqi society was torn as a result of that," Kilcullen said.

[On Monday, Iraqi and U.S. troops killed and captured members of a network that facilitated the transport of weapons and explosives from Iran to Iraq. The network, based in Baghdad, also brought insurgents from Iraq to Iran for training.] The first step in the Al Qaida campaign has been to infiltrate Sunni areas. The infiltration begins with the arrival of Al Qaida-aligned clerics who demand a pulpit and take over mosques and schools.

With a base of operations, Al Qaida then attacks neighboring Shi'ite communities. The strikes, usually suicide bombings in public places, result in retaliation by Shi'ite militias.

"Those sectarian attacks polarize the community," Kilcullen said. "They create tensions that make it very difficult to make progress on political reconciliation, and they further intimidate the Sunni communities, which tend to sort of close ranks in the face of the external threat."

At that point, officials said, Al Qaida helps establish militias to protect against Shi'ite attacks. These networks, financed by Al Qaida, include criminals, foreign fighters and the unemployed.

Kilcullen said the U.S. military has sought to halt the flow of funds from smuggling and black market operations to Al Qaida networks. He said the effort has been focused on Baghdad, which contains a major Al Qaida presence in Sunni neighborhoods.

"Even if the extremists do manage to infiltrate, we're trying to make it harder for them to attack the neighboring Shia communities," Kilcullen said.

Kilcullen said the U.S. military has gated Sunni neighborhoods to secure them from Al Qaida infiltration. He said the walls constructed around these areas have reduced the flow of insurgents and weapons and increased the feeling of security.

Officials have reported a steady reduction in sectarian violence in Baghdad. They cited 20 casualties per day, from 130 in late 2006.

"The negative effect of imposing this barrier, I think, is outweighed by the negative effect of lots of people getting killed," Kilcullen said.