Three Syrian men were arrested Thursday in Germany on suspicion of planning a terror attack on Dusseldorf on behalf of ISIS, the German attorney general's office said. The cell - which allegedly included an experienced bomb maker - was plotting a mass casualty attack on the old town of the western German city, using suicide vests and guns, federal prosecutors say. There were no indications that the plot, believed ordered by senior ISIS leadership, was in an advanced stage of implementation, the statement said. The three were apprehended separately Thursday in the states of North Rhine-Westphalia, Brandenburg and Baden-Wurttemberg, the attorney general said in a statement. The homes of the men - identified only as Hamza C., 27; Mahood B., 25; and Abd Arahman A. K., 31 - are being searched for evidence. German officials have requested extradition of a fourth suspect, a 25-year-old Syrian national named Saleh A., who has been in French custody since February. Information that the fourth suspect disclosed to French authorities led to the arrests, the statement said.