After a nearly four-year probe, the CBI has filed a closure report in a case related to alleged irregularities in the allotment of Kilhoni coal block in Maharashtra to Nippon Denro Ispat Limited in 1998, officials said on Tuesday. The agency had started the preliminary enquiry on the directions of the Central Vigilance Commission in 2012 where a complaint was filed by then Congress MP Sandeep Dikshit and six other then MPs alleging irregularities in the allocation of coal blocks during the period 1993-2005.