(CNN) Family members of US service members who were killed or wounded in Afghanistan sued a number of prominent contractors on Friday that worked to rebuild the country post-invasion, accusing them of funneling millions of dollars in payments to the Taliban for protection that funded the group's attacks on American troops in the region.

The suit, filed in Washington, DC, federal court, said the funds from the development and private security firms were part of a "common practice by certain corrupt contractors" that sought to save money on security by paying off the Taliban

The firms allegedly used a network of subcontractors and private security groups to transfer cash to Taliban agents, and in some cases dole out salaries to certain Taliban "guards" between 2006 and 2014, while the group was allying with al Qaeda and waging a violent campaign against US forces and their allies, according to the lawsuit.

"Defendants decided that buying off the terrorists was the most efficient way to operate their businesses while managing their own security risks -- even though doing so jeopardized other American lives," the lawsuit says.

"Those protection payments aided and abetted terrorism by directly funding an al-Qaeda-backed Taliban insurgency that killed and injured thousands of Americans," the suit added.

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