French defence firm Dassault picked Reliance Group, run by Indian billionaire Anil Ambani, as its main local partner in the multi-billion-dollar 2016 deal to buy 36 Rafale jets, instead of the state-run Hindustan Aeronautics Limited (HAL).

This has long been controversial because unlike HAL, Reliance had no previous experience in the aeronautics sector.

Hollande, president from 2012-17, was quoted on Friday by investigative website Mediapart as saying that France was given no choice on Dassault's Indian partner.

"We did not have a say in that," Hollande was quoted as saying. "It was the Indian government that proposed this service group (Reliance), and Dassault who negotiated with Ambani.

"We did not have a choice, we took the interlocutor who was given to us."

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The comments were front-page news in Indian newspapers on Saturday and was the top trending topic on Twitter.

Rahul Gandhi, head of the main opposition Congress party, who is seeking to replace Modi and his rightwing Bharatiya Janata Party (BJP) in elections next year, went on the offensive.

"An ex-president of France is calling him (the prime minister of India) a thief. It's a question of the dignity of the office of the prime minister," he told a news conference in New Delhi.

"The PM has betrayed India. He has dishonoured the blood of our soldiers," Gandhi, scion of India's Gandhi-Nehru political dynasty, added on Twitter.

Ravi Shankar Prasad, a close Modi ally and minister, hit back at Gandhi, accusing him playing into the hands of India's rivals Pakistan and China.

"Never before in the history of independent India has a party president used such words for a PM," he told a news conference on Saturday.

"We can't expect anything else from Rahul Gandhi. He has no quality or ability."

India's defence ministry tweeted on Friday that neither the Indian nor French government "had any say in the commercial decision".

On Saturday the ministry issued a fuller statement, saying no rules were broken.

"The government of India has no role in the selection of Indian offset partner," it said.

Foreign manufacturers securing arms contracts in India -- the world's biggest defence importer -- are obliged to reinvest a portion of the sums collected in India under the offset rule to encourage local defence manufacturing.

The defence ministry also cited a statement from Dassault saying it had signed partnership agreements with several companies and was negotiating with around 100 other companies.

Under the Rafale deal, France must spend amounts totalling around half the eight billion euros ($9.4 billion) paid by the Indian government.

Dassault has invested more than 100 million euros in its joint venture with Reliance.

Hollande also denied any conflict of interest with Reliance, which partially financed a film by his partner Julie Gayet in 2016.

"That is why, moreover, this group (Reliance) did not have to give me any thanks for anything. I could not even imagine that there was any connection to a film by Julie Gayet," Hollande said.