CBI sources said the agency has re-registered 18 FIRs in connection with these land deals, which were earlier probed by the Rajasthan Police.
"The cases pertain to fraudulent and fictitious claims and allotments in lieu of land acquired for Mahajan Field Firing Range Bikaner, which is used by the Army," a CBI spokesperson said in New Delhi after the cases were registered this evening.
Among the 18 FIRs registered by the agency, 16 were lodged at the Gajner police station while two at Kolayat police station in Bikaner between August and September, 2014, agency sources said.
The cases were referred to the CBI by the Centre on the request of the Rajasthan Government.
The Rajasthan government had written to the CBI for a probe into alleged land scams in Bikaner, including those involving a company linked to Congress president Sonia Gandhi's son-in-law Robert Vadra.
The Congress had accused the state government of misusing the CBI ahead of assembly elections.
"As many as 18 FIRs are registered. Four of them are against Vadra's company which were allegedly involved in illegal purchase of nearly 275 bigha land. All the 18 FIRs are in connection with the purchase of close to 1,400 bigha land in fake names," Rajasthan Home Minister Gulab Chand Kataria had said on August 22 after referring the matter to the CBI.
He had alleged that Mr Vadra's company was the third party to purchase 275 bigha of land in 2010 and it sold it to a fourth party in 2012.
"When the matter came to light, 18 FIRs were registered. Four FIRs are related with Vadra's company and now the state government has written to the CBI to investigate them altogether. The issue was also raised in the state assembly in 2014," Mr Kataria had said.
Reacting to this, state Congress president Sachin Pilot had said, "BJP misuses CBI, ED (Enforcement Directorate) and other agencies for political gains. In this alleged land scam case, the state government had formed a committee but the committee's findings were not disclosed by the government."
He had said, "Those who have been arrested in the land scam are connected with BJP. If BJP people are being arrested in the land scam, then we are ready for any probe."
The state government had on December 31, 2014 cancelled 18 mutations (transfer of ownership) in Bikaner after allegedly finding them to be illegal.
It is alleged that the land was illegally allotted or possessed in 2006-07 by some villagers, who were "wrongfully" shown as farmers displaced by the acquisition of land for the Mahajan Field Firing Range for the Army.
It was alleged that Mr Vadra's company also purchased chunks of land.
However, the farmers who were actually displaced were allotted land between 1992 and 1996.