The CBI has asked the Defence Ministry to blacklist six firms, including four international ones, for their alleged involvement in the Ordnance Factory Board scam. <br/><br/>Official sources said, the names of four international companies, Singapore Technologies Kinetics, Israel Military Industries Ltd, Rheinmetall Air Defence, Zurich, and Cooperation Defence, Russia are mentioned in the letter by the CBI to the Defence Ministry. <br/><br/>Besides, two Indian firms, T S Kisan and companies Pvt Ltd, New Delhi and R K Machines Tools Ltd, Ludhiana, have also been named in the CBI communique to the Ministry of Defence sent earlier this week. <br/><br/>The action came after agency sleuths investigating the case found alleged involvement of these firms in the scandal.<br/><br/>The agency had on June 30 filed a 2,700-page chargesheet in a special CBI court, Kolkata, against former Director General of Ordnance factory Board, Sudipta Ghosh and 11 others for graft. <br/><br/>A case was registered by CBI on May 17, 2009 under different Sections of IPC and Prevention of the Corruption Act against Ghosh and others.