Breaking from its standard practice, CBI today questioned corporate lobbyist Niira Radia for four hours at her residence in south Delhi in connection with the 2G spectrum allocation scam.

CBI's move to question Radia at her farmhouse raised eyebrows as the agency had yesterday issued summons asking her to appear before the agency. Usually, those summoned are questioned at the CBI headquarters or its offices here.

Seeking to downplay the issue, CBI spokesperson said, "I dont have much to say but it is the prerogative of the Investigation Officer to choose the place for questioning.

There have been instances earlier as well when CBI has gone to a person's place for questioning."

CBI reached Radia's farmhouse at Chhattarpur area at about 10 am to question her on several issues including her alleged involvement in the spectrum allocation.

Her questioning was being carried by the CBI probing a case registered on October 21, 2009 against unknown Department of Telecom officials and private persons and companies for allegedly causing loss of Rs 22,000 crore to the exchequer.

The figure of the loses mentioned in the agency's FIR were based on the findings of Central Vigilance Commission which had referred the case to the CBI.

The CBI sleuths had earlier carried out searches at Radia's residence and the premises of her firm, Vaishnavi Communications, here.

The Enforcement Directorate (ED) has also grilled her on allegations of money laundering last month when she was called to the ED headquarters.

Radia hit the spotlight after her taped telephonic conversations with various influential people including industrialists, politicians and journalists became public.

Supreme Court is closely monitoring the multi agency probe in the allocation of 2G spectrum to certain telecom firms.

It has criticised the CBI for its slow pace in the probe and had asked why none of the high-profile people including former Telecom Minister A Raja not being questioned so far.

CBI has issued summons to Raja, who is in Chennai, asking him to appear before the agency.

The apex court has asked CBI and ED to submit status reports on their probe to it by February 10, when the 2G spectrum case will come up for hearing.

The Comptroller and Auditor General of India (CAG) in its report to the Parliament had said that the allocation of 2G spectrum at under valued prices had resulted in the loss of Rs 1.76 lakh crore to the exchequer.