“If there is evidence, if there are results of the investigations that would justify an intervention from us, then we will do that,” Darabos said.

A spokesman for the Austrian defence ministry said options could be considered ranging from a claim for damages to outright cancellation of the deal.

EADS declined to comment.

Austria, which describes itself as neutral, does not fight wars but does take part in peacekeeping and humanitarian military operations and is obliged to maintain a flight of jets to patrol its airspace.

The Defence Ministry has written to state prosecutors asking what the legal implications would be if bribery were found to have been involved in the Eurofighter deal, and excerpts of the letter were published on Friday by Austria’s Der Standard.

The ministry spokesman confirmed the excerpts were accurate and added the Eurofighter purchase contract included a get-out clause in case of bribery.

All 15 jets have been delivered and paid for, although the Austrian government still has 434 million euros of payments outstanding to financing bank BAWAG.

Austria’s Economy Ministry, which is responsible for approving the counter-trades, said it was awaiting the results of prosecutors’ investigations. It has engaged an external auditor to check all the contracts signed from 2006 onwards.

Peter Pilz, an opposition Green lawmaker who has been pursuing the Eurofighter side deals for years, said he estimated 80-90 percent of them were corrupt.