Gandhi's latest salvo came following French website Mediapart on Wednesday reporting that Reliance Defence was given to Dassault Aviation, manufacturer of the Rafale jets, as an "obligatory" offset partner for the deal announced by Modi in April 2015.
"The Prime Minister of India is corrupt," Gandhi said at a special media briefing here.
Questioning Modi's "deafening silence" , despite allegations of corruption directed at him, Gandhi said the Prime Minister must resign.
"Allegations of corruption are being directed at him and the Prime Minister is silent. He should resign if he cannot respond (to the charges)," he said.
Gandhi also read out excerpts from Mediapart report, which quoting Dassault's Chief Operating Officer Loik Segalen, said that the choice of the Indian private entity was a "compensation" for the purchase of the fighter jets.
"What is he being compensated for," asked Gandhi alleging that "Modi put Rs 30,000 crore in his industrialist crony's pockets."
"Ex-President of France (Francois Hollande), no less, has said that India's PM is corrupt, now the company which got the contract, its senior executive is saying that India's PM is corrupt," said Gandhi, pointing to the French website's earlier report quoting Hollande as saying that India had proposed the Indian private entity as the partner for the deal.
Gandhi said it was a "clear-cut case of corruption" against Modi and ridiculed the BJP government for shying away from a Joint Parliamentary Committee probe (JPC) into the deal.
On Dassault reiterating that it "has freely chosen to make a partnership with India's Reliance Group", Gandhi said the jet manufacturer was "sitting on a huge contract and will say what the Indian government wanted it to say".
Gandhi also questioned the motive behind Defence Minister Nirmala Sitharaman's three-day visit to France, alleging that there was a "huge cover-up going on" and the "media was being pressured".
"The great Rafale cover-up has begun. To try and show the deal is legitimate, Raksha Mantri will need to generate minutes of imaginary meetings held between the French and our Ministry of Defence and both sides will need to agree on a common story to be spun to the media," said Gandhi about Sitharaman's visit beginning Wednesday.
He said the country will soon realise the "truth about Modi" who came to power on the expressed promise of fighting corruption.
Alleging massive irregularities in the deal, the Congress has twice petitioned the Comptroller and Auditor General of India for a special and forensic audit and also moved the Central Vigilance Commission seeking a probe and seizure of relevant documents pertaining to the deal.It has also been persistent in demanding a JPC probe.
Besides questioning the "inflated" price of the jets, the Congress has also been targeting the Centre over the propriety of a newly-founded private company getting the Rs 30,000 crore Rafale offset contract at the cost of the state-owned Hindustan Aeronautics Ltd (HAL).
Gandhi is slated to meet HAL employees on Saturday at the defence PSU headquarter in Bengaluru.
Hitting back, the BJP accused Gandhi of mocking and jeopardising national security.
"He is trying to build his political career by spreading lies on Rafale," BJP spokesperson Sambit patra said, alleging the entire Gandhi family was "corrupt".
Patra dared Gandhi to produce evidence to prove his allegations that Hollande had called Modi corrupt.