Agency officials have confirmed Parakh will be called to the CBI headquarters next week. This will be Parakh's first questioning since the registration of the first information report.

The CBI must file a status report on the probe in the Supreme Court by the end of April.

In his book, Crusader or Conspirator? Coalgate and Other Truths, Parakh made a personal attack on CBI Chief Ranjit Sinha.

He accused Sinha of abusing his position, and acting without proper understanding of facts, rules and laws.

Sinha hit back, telling UK media he was amused that Parakh, an accused in one of the coal cases, was seeking answers from the CBI.

Sinha told the Daily Mail: "He should not indulge in investigation, that is our job. He has been a policy maker, he should stick to that." This was in response to Parakh's claim that the case could go the Bofors way as the CBI wad not on the right track

He went on to remind Parakh that it will be the CBI asking the questions when the former bureaucrat is interrogated for his alleged involvement in the coal scam.

With Parakh getting support from the Indian Administrative Service fraternity, including former Comptroller and Auditor General Vinod Rai, the issue has turned into an IAS vs Indian Police Service clash.

Parakh's outrage was initially fuelled by CBI officers who searched his house in October.

CBI has alleged that during 2005, there was a criminal conspiracy and the then coal secretary abused his position and showed undue favour to the Odisha-based industry in allocation of Talabira II and Talabira III coal blocks along with a public sector undertaking of Tamil Nadu.

After completing the investigations in the case, the CBI will make a decision whether to go ahead with filing a charge-sheet or move a closure report in the court.