CBI is examining a letter written by BJP leader Arun Jaitley levelling corruption allegations against Himachal Pradesh Chief Minister Virbhadra Singh and does not rule out the possibility of examining the Congress veteran at a later stage.

Jaitley, leader of opposition in Rajya Sabha, had written the letter to Prime Minister Manmohan Singh and marked a copy to CBI Director Ranjit Sinha making various corruption allegations against Virbhadra Singh including that he received pay offs of over Rs two crore from a private steel firm during his tenure as Union Steel Minister.

Virbhadra Singh has denied all charges and said that he was ready for a probe by any agency.

Official sources said they were examining the letter written by Jaitley as the agency had already included the allegations levelled against Singh in a Preliminary Enquiry registered last year at the request of State Trading Corporation which had called for a CBI probe.

The STC had requested for a probe as Income Tax department had recovered a set of documents from a Mumbai- based steel firm which alleged pay off to various ministries and some of the entries were marked against initials of 'VBS' and 'MoS APS'.

There were four entries made to the listed beneficiary -- 'VBS'--which totalled up to Rs 2.8 crore from October, 2009 to October, 2010.  Singh was Steel Minister from May 28, 2009 to January 18, 2011.

The CBI, which is probing the case, did not rule out the possibility of examining Singh and his family members in connection with the case, they said.