ROME (AFP) - The head of Italian defence and aerospace giant Finmeccanica, Giuseppe Orsi, resigned on Friday in a bribery scandal over the sale of helicopters to India as investigators questioned him in prison.

Orsi, who was arrested on Tuesday over alleged bribes paid to secure the sale of 12 choppers, also stepped down as a member of the board and presented his resignation letter to judge Luca Labianca, who heard his testimony behind bars.

His lawyer said the resignation was aimed at "calming the climate created by the probe" into Orsi and the former head of its helicopter division Agusta Westland, Bruno Spagnolini, who is also due to be interrogated.

"I never knew anything about illicit operations," Orsi said according to his lawyer, adding that he had never met members of the "Tyagi family" - the alleged recipients of the bribes according to leaks in Italian media.

Bribes amounting to 20 million euros (S$33 million) were paid through two Switzerland-based intermediaries, Guido Haschke and Carlo Gerosa, who are officially fugitives, Italian media said citing investigative documents.

The total of 30 million euros in bribes were paid for the 556-million-euro contract, investigators believe.

Investigators say payments were made through Tunisia-registered companies controlled by Haschke and Gerosa and were then transferred to accounts in India and Mauritius belonging to a company called Aeromatrix, the reports said.

"The money was destined for intermediaries and to remunerate corrupt public officials," Orsi's arrest warrant was quoted by Il Messaggero daily newspaper as saying.

Italian police have so far arrested two people, Orsi and Spagnolini, and carried out 37 raids including on their homes and offices.

The two are accused of international corruption and tax fraud.

Italian prosecutors have requested the extradition of Haschke and Gerosa.

During a raid on the house of Haschke's mother, La Repubblica daily newspaper said police had found details of a plan to pay an Indian general referred to as "Saini" a 0.5-percent commission, around five million dollars, for a helicopter deal.

The discovery was first reported by Il Fatto Quotidiano daily.

La Repubblica quoted from a transcript of a bugged phone conversation involving Orsi in which the CEO could be heard saying: "They're talking about the Indian general? Shit, are they talking about the 0.5 percent?".