Kolkata, Sep 22 (IANS): Senior Congress leader and former union minister Abu Hasem Khan Chowdhury Monday appeared before the CBI on being summoned in connection with the multi-crore-rupee Saradha scam and was questioned for nearly three hours.

Chowdhury, who represents West Bengal's Malda South Lok Sabha constituency, said he was questioned about the letters he had written to then prime minister Manmohan Singh about the Saradha Group.

"I was asked about the letters that I had written to the prime minister," he told media persons after coming out the Central Bureau of Investigation (CBI) office here.

During the day, CBI sleuths also interrogated officials of several banks, including State Bank of India, in connection with the scandal.

Reacting to Chowdhury's summoning, state Congress president Adhir Ranjan Chowdhury said it was not a matter for concern for the party.

"Calling for questioning doesn't mean he has been made an accused. We have been supporting the CBI probe and extend all cooperation to it. It's not a matter of concern," he said.

Abu Hasem Khan Chowdhury, who had drawn the attention of Manmohan Singh to the mushrooming Ponzi schemes in West Bengal and urged action against them, later retracted and batted for the tainted Saradha Group.

Contradicting his September 2011 letter to Manmohan Singh, he in March 2012 wrote to the prime minister again, saying: "The company (Saradha) is conducting a prosperous and successful realty business in West Bengal with some investment in the media and health sectors", and sought withdrawal of his earlier complaint.

But after the scam came to light, Chowdhury admitted batting for the Saradha Group was a "mistake".

Having arrested four people, including Trinamool Congress leader and former IPS officer Rajat Majumdar, the CBI recently questioned Communist Party of India-Marxist leader Rabin Deb in connection with the scam.