The CBI on Tuesday registered cases against five companies and unknown government officials as part of its probe into alleged irregularities in allocation of coal blocks and carried out searches across 10 cities.

According to CBI spokesperson, five FIRs have been filed against five companies and unknown government officials for alleged cheating.

The agency sleuths were also conducting searches at 30 places in ten cities including Delhi, Mumbai, Kolkata, Patna, Hyderabad, Dhanbad and Nagpur, the spokesperson said.

The filing of FIRs comes three months after registration of a Preliminary Enquiry into the coal scam by the agency on the directions of the Central Vigilance Commission.

During the Preliminary Enquiry, the CBI was informed by the Coal ministry officials that it had issued show cause notices to some of the firms which were allocated the mines for explaining the delay in conducting the mining work.

Some of the firms, which were allocated coal blocks in 2005, were yet to start mining, official sources said.

The CBI had also examined the past areas of operation of some of the companies which were allotted coal blocks in Jharkhand, Chhattisgarh and Karnataka, the sources said alleging some of these firms had been set up only for getting coal blocks allocated and the same was later sublet to other companies at a premium.

The agency has already questioned senior bureaucrats who were overseeing allocation of coal blocks during 2005-09, the sources said.

They said the questioning of the Coal Secretaries, who also chair the screening committee, was done to understand the issues involved in the allocation of coal blocks during the period and so far the agency has not found any irregularities on their part.