An Indian court on Thursday ordered police to complete a probe into charges that a bribe was paid in a multi-billion dollar deal to buy Scorpene submarines from a French defence firm.

The Delhi High Court told the Central Bureau of Investigation (CBI) to complete its inquiry within three months and report back to a two-judge bench.

The judges also told the CBI to press criminal charges against "accused persons" if it could establish an offence had been committed in the 2.4 billion euro (three billion dollar) deal.

"In case CBI decides to close the case after the inquiry then it will have to satisfy the court that there was no evidence of kickbacks involved in the deal," judges T. S. Thakur and Veena Birbal said.

The order came a month after an Indian pressure group — the Centre for Public Interest Litigation — alleged New Delhi was shielding Indian middlemen who took commissions from French defence giant Thales, which owns Armaris, to clinch the deal.

Thales and the French government have denied the allegations.

Prashant Bhushan, who heads the pressure group, told the court that he doubted the intentions of the CBI, which had earlier this year abandoned an investigation into the bribery allegations.

"It has not done anything during the last 21 months and we fear it would submit a report without conducting a proper inquiry… We demand a full-fledged investigation," Bhushan said.

India in October last year signed contracts worth 2.4 billion euros with Armaris and European defence firm MBDA to buy six of the Franco-Spanish submarines.

The deal is a technology transfer agreement.

The Scorpenes will be assembled in India, but French naval group Direction des Compagnies Navales (DCN) will produce various key parts that require equipment unavailable at Indian shipyards.

India's main opposition Bharatiya Janata Party party has also alleged that four percent of the contract amount, estimated to be 100 million dollars, was paid to the brokers, one of whom is said to be close to the ruling Congress party.

Earlier this month, India said it was scrapping a 600-million-dollar deal to buy 197 military helicopters from the European Aeronautic Defence and Space Company (EADS) after allegations of corruption in the bidding process.

India banned middlemen in military deals following charges of bribery in a multi-billion-dollar artillery deal in the 1980s with Swedish firm Bofors.

That scandal led to the downfall of the government of Congress prime minister Rajiv Gandhi in 1989.