Apart from the 12 private persons, formal FIRs were also registered against four companies, CBI sources said Wednesday.

The firms are Finmeccanica, AgustaWestland, IDS Infotech Ltd (India) and Aeromatrix India.

Former Air Force chief S P Tyagi. File Pic/AFP

The country's premier probe agency has also raided 14 places in the National Capital Region, Delhi and Chandigarh.

A CBI and defence ministry team had gone to Italy to collect documents concerning alleged kickbacks to clinch the deal.

The investigative agency filed a preliminary inquiry against 11 people Feb 25.

Investigations are on into bribery allegations in the Rs 3,600 crore deal for 12 AW-101 choppers.

Former Finmeccanica CEO Giuseppe Orsi was arrested Feb 18 by Italian authorities on suspicion of engaging middlemen to swing the deal in his firm's favour.