Brazilian prosecutors have agreed to open an inquiry into a multi-billion-dollar tender pitting France, the United States and Sweden to supply the Latin American nation with modern fighter jets.

A prosecution source told AFP Wednesday that prosecutor Jose Alfredo de Paulo Silva approved the request from a Brazilian individual who argued the preference for France's Rafale was against "economic principles."

The finalists now battling it out in the final stages of the tender are France's Rafale made by Dassault, Sweden's Gripen NG by Saab, and the F/A-18 Super Hornet manufactured by US giant Boeing.

But President Luiz Inacio Lula da Silva's stated preference for the ultra-sophisticated, semi-stealth Rafale jet has angered the air force, which preferred the much cheaper and easier-to-maintain Gripen.

The Rafale has never been sold abroad, but after Lula's comments is now seen as the front-runner to clinch the contract to supply some 36 fighter jets to the South American nation.

"The Brazilian government, because of external political factors, has decided to choose the Rafale, ruling out the Gripen and Super Hornet which were put forward at a lower price. That is against economic principles," the Brazilian opponent said.

A spokesman for interior ministry told AFP the prosecutor would now "gather information to decide whether... there is a civil case to answer." The inquiry could last as long as a year, the source added.

On Monday, officials said Lula had now put off any announcement on the winner of the bid, which had been due after Easter, until mid-May.

Throughout the competition, Lula and Defense Minister Nelson Jobim have underscored technology transfer as their top priority so that Brazil could not only build its own next-generation fighters but also export them.

France's jet bid was bolstered by the fact that Brazil has a strategic pact with Paris that has already seen it sign a 12-billion-dollar deal in early 2009 to buy 50 helicopters and five submarines from France.