In a communication sent recently through diplomatic channels, the government is believed to have assured the Swiss authorities that the documents being sought would not be used for political purposes.

The letter is understood to have told the Swiss government that the papers would be basically used to prosecute those suspected to be involved in bribery and corruption in the gun deal.

One of the appellants in the Swiss courts seeking to block the transfer of documents to India had recently appealed to the Swiss Federal Council that the papers should not be sent to India because they would be used for political purposes.

Meanwhile, sources said the Central Bureau of Investigation (CBI) is preparing to file a supplementary charge-sheet in the case against Madhavsinh Solanki, who as external affairs minister had allegedly passed on a letter to his Swisscounterpart in the early nineties on behalf of one of the recipients of bribes with the intention of stopping the transfer of documents.

However, there has been no charge of Solanki having received any money in return.

Recently, the CBI filed a charge-sheet in the case which was caught in a high-voltage controversy as the agency had named late Rajiv Gandhi as an accused and put his name in column 2 of the charge-sheet as he was not being sent for trial.