NEW DELHI: Detectives raided the home of India's former air force chief on Wednesday as part of an investigation into alleged bribes paid to secure a $748 million contract for 12 Italian helicopters.

Central Bureau of Investigation (CBI) spokeswoman Dharini Mishra said former air chief marshal S.P. Tyagi's home was among more than a dozen addresses targeted in the raids.

“He is one of the 13 people we have filed an FIR (First Information Report) against,” Mishra told AFP.

The FIR filed on Wednesday represents the first stage of an official police enquiry.

The CBI had filed a “preliminary enquiry” report last month into the alleged scandal, linking four companies, four Westerners and seven Indians to the bribery allegations.

Mishra said investigators had raided a total of 14 locations in the northern cities of New Delhi, Chandigarh, and Gurgaon.

India put payments to the Italian company Finmeccanica on hold last month and threatened punitive action against the firm if any wrongdoing was uncovered.

The Indian government also agreed to set up a joint parliamentary commission which would include opposition lawmakers to probe charges that bribes were paid to swing the deal in favour of Finmeccanica's British unit AgustaWestland.

The helicopter purchase came under scrutiny from Italian investigators looking into allegations the group had broken the law by paying bribes to foreign officials, leading to the arrest of Finmeccanica's boss Giuseppe Orsi.

Orsi, who quit after his arrest, denies any wrongdoing and his lawyer has called his arrest “unjustified”.

Italian prosecutors suspect that kickbacks worth around 10 per cent of the deal, or 50 million euros ($68 million), were paid to Indian officials to ensure AgustaWestland won the contract, according to Italian media reports.

Cash was allegedly handed to a cousin of the former Indian air force chief with more money funnelled via a web of middlemen and companies in London, Switzerland, Tunisia and Mauritius.

The chopper deal was cleared by Indian Prime Minister Manmohan Singh, whose Congress-led government has been buffeted by a series of corruption scandals that analysts say could affect the party's electoral chances in 2014 polls.

India has already received three of the choppers. The rest were to be delivered by the end of 2014.