The Paris public prosecutor opened a preliminary investigation after French naval contractor DCNS filed a complaint for breach of trust over a leak of documents concerning six Scorpene submarines it is building for India, a judicial source said.

DCNS was left reeling after details from more than 22,000 pages of documents relating to submarines it is building for India were published in The Australian newspaper this week, sparking concerns about the company's ability to protect sensitive data.

"We filed a complaint against unknown persons for breach of trust with the Paris prosecutor on Thursday afternoon," a spokesperson for the shipbuilder said yesterday.

The Paris prosecutor's office opened an investigation for breach of trust, receiving stolen goods and complicity, the judicial source said later yesterday.

A French government source said on Thursday that DCNS had apparently been robbed and it was not a leak, adding it was unlikely that classified data was stolen.

The Australian government said yesterday it had asked DCNS to take new security measures in Australia, where the company is locked in exclusive negotiations to build a new fleet of submarines for A$50 billion (US$38 billion).

DCNS said earlier this week that the leak, which covered details of the Scorpene-class model and not the vessel currently being designed for the Australian fleet, bore the hallmarks of "economic warfare" carried out by frustrated competitors.

- Reuters