Government officials involved in the process may be called for recording their statements, sources in CBI said.
"The probe is on. CBI will begin questioning of directors (of firms named in FIRs) and other officials of the company from next week. Some bureaucrats may also be called in," they said.
Those named in the FIRs against JLD Yavatmal Energy Ltd, JAS Infrastructure Capital Private Ltd and AMR Iron and Steel are likely to be called first for questioning, the sources said.
Besides this, the agency would also question persons named in FIRs against Nav Bharat Power Private Ltd and Vini Iron and Steel Ltd.
CBI teams have scrutinised data on laptops, hard drives and other documents collected during its raids at various locations across the country and scrutinising them.
The agency had on September 4 registered five cases in connection with the alleged scam in allocation of coal mines and conducted country-wide searches at nearly 30 places.
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CBI, which had registered a Preliminary Enquiry (PE) in June, has slapped charges of cheating and suppression of facts against the companies.
The filing of FIRs comes three months after registration of a PE into the alleged coal scam by the probe agency on the directions of the Central Vigilance Commission.