The income tax department has found "undisclosed" income of more than Rs 250 crore after it raided two "prominent" real estate groups based in Kolkata, West Bengal, the CBDT said on Wednesday.

The searches were launched on August 18, it said.

The department gathered "evidences of out-of-books cash transactions and on-money receipts and several documents and electronic data indicate routing of unaccounted money through shell companies".

Documents found during the operation indicate use of unaccounted funds in land acquisition, the Central Board of Direct Taxes (CBDT) alleged.

The CBDT, which frames policy for the tax department, did not identify the groups raided.

"The key persons (of the groups) admitted use of shell (bogus) companies for infusion of unaccounted funds in the form of share capital, share premium and unsecured loans through sale of bogus investments," the CBDT said in a statement.

The raids, so far, led to a detection of unaccounted income of more than Rs 250 crore, the statement said, adding 16 bank lockers have been sealed.