HOUSTON (AP) — Four men have pleaded guilty in Houston to participating in a fraud and money laundering scheme that used a network of call centers in India.

Acting U.S. Attorney Abe Martinez in Houston says individuals at call centers in Ahmedabad, India, impersonated IRS and immigration authorities and threatened victims around the U.S. to use gift cards or wire money to make payments they contended were owed to the government.

U.S.-based "runners" then would liquidate or launder the fraudulent proceeds.

Three men — 26-year-old Nisarg Patel, of Flemington, New Jersey; 30-year-old Dilipkumar Patel, of Ocala, Florida; and 39-year-old Rajesh Kumar, of Mesa, Arizona — pleaded guilty Friday in federal court in Houston. Another man, 38-year-old Dipakkumar Patel, of Pennsylvania, pleaded before a federal judge in Georgia. All are in custody awaiting sentencing.