Congress president Rahul Gandhi Thursday demanded an investigation against Prime Minister Narendra Modi on role in the Rafale deal, alleging that he was a "corrupt man" who helped Anil Ambani pocket Rs 30,000 crore in the purchase of  36 aircraft.

Gandhi's demand for a probe came a day after a report in French publication that said Dassault Aviation, the manufacturer of Rafale, had to choose Ambani's firm Reliance Defence as its offsets partner in India as a trade-off for getting the deal.

The government has been insisting that it had no role in Dassault's choice of Reliance Defence.

The Congress president also described Defence Minister Nirmala Sitharaman's three-day trip to France from Thursday as part of a "huge cover-up" by the government on the Rafale deal.

"Why has suddenly the defence minister rushed to France? What is the emergency?" Gandhi asked at a press conference.

"The reality is the prime minister is corrupt. The prime minister of India is a corrupt man," he said.

Modi came to power on the promise of fighting corruption, the Congress leader said, adding that he wanted to tell the youth of the country that the prime minister was involved in corruption.

On Wednesday, French investigative publication Mediapart, citing an internal document of Dassault Aviation, reported that the aerospace giant was forced to enter into a  joint venture with Reliance Defence as part of a trade-off to bag the contract for the 36 Rafale jet deal.

Dassault Aviation said in a statement that it has "freely chosen to make a partnership with India's Reliance Group".

Last month, Mediapart quoted former French president Francois Hollande as saying that France was given "no choice" on selection of the Indian partner for Dassault and the Indian government proposed the name of the Indian company to partner with the French aerospace giant.

The report triggered a massive political row with Congress escalating its attack on the government and the government firmly rejecting the charges.

Both Dassault and Reliance Defence have already announced setting up of a joint venture to manufacture aerospace components and fulfil offset obligations for the Rafale deal.

Under India's offset policy, foreign defence entities are mandated to spend at least 30 per cent of the total contract value in India through procurement of components or setting up of research and development facilities.

The Congress has been alleging massive irregularities in the deal, saying the government was procuring each aircraft at a cost of over Rs 1,670 crore as against Rs 526 crore finalised by the UPA government when it was negotiating the procurement of 126 Rafale jets.

The opposition parties have alleged Reliance Defence was formed just 12 days before the announcement of the Rafale deal in 2015. Reliance group has rejected the charges.

The Congress has also been demanding answers from the government on why state-run aerospace major HAL was not involved in the deal as finalised during the UPA.

In its reaction following the Mediapart report, Dassault Aviation said, "In compliance with the Indian regulations (Defence Procurement Procedure) and as frequent with such a contract, Dassault Aviation has committed to offsets in India worth 50 per cent of the value of the purchase."

"In order to deliver some of these offsets, Dassault Aviation has decided to create a joint-venture. Dassault Aviation has freely chosen to make a partnership with India's Reliance Group," it said.

The French aerospace major said partnerships have also been signed with other companies such as BTSL, DEFSYS, Kinetic, Mahindra, Maini and SAMTEL.

"Other negotiations are ongoing with a hundred-odd other potential partners," it said.