A fighter jet deal between India and France is at the centre of a political storm in India, as the opposition Congress party led a march in Mumbai on Thursday to protest against alleged improprieties over the US$8.7 billion (S$11.9 billion) deal.
This comes as political parties in India gear up for state elections in Rajasthan, Madhya Pradesh and Chhattisgarh this year and a general election next year.
"The Rafale scam has begun to stink and Mr Modi has begun to sink," Congress leader Jaipal Reddy said on Thursday.
The controversy is over India's purchase of 36 Rafale fighter jets from French firm Dassault Aviation, a deal struck during Prime Minister Narendra Modi's visit to France in 2015.
Congress has questioned the choice of businessman Anil Ambani's Reliance Defence as Dassault's local partner instead of the original choice of state-run manufacturer Hindustan Aeronautics.
They note that Mr Ambani is close to Mr Modi, and that Reliance Defence was set up only in 2015 and not as experienced as Hindustan Aeronautics.
Under Indian rules for defence acquisition, a foreign firm has to put in at least 30 per cent of the contract in India as part of the country's efforts to build up domestic defence manufacturing.
Earlier this month, former French president Francois Hollande, who was in power when the deal was signed, said it was the Indian government that had chosen Mr Ambani's company.
"We did not have a say in this... The Indian government proposed this service group and Dassault negotiated with the Ambani group. We did not have a choice, we took the partner who was given to us," he told French-based journal, Mediapart.
The current French government said it did not want ties with India to be affected by the controversy.
French President Emmanuel Macron told ANI news agency on Wednesday: "That's a government-to-government discussion. We have a very strong partnership between India and France regarding defence. I don't want to comment on any other thing."
Mr Modi's Bharatiya Janata Party (BJP) has denied any wrongdoing and said the deal was part of efforts to bulk up India's defence capabilities.
India's defence ministry said in a statement that neither the French nor the Indian governments had a say in the commercial decision.
Dassault Aviation had also said that the contract with the Indian partner was its choice.
Political analysts said Congress has gone on a fierce attack, as it had sniffed an opportunity to corner the government on the Rafale deal. But they said it remained to be seen if the issue resonated with voters.
The Congress party was itself plagued by a series of corruption scandals, including over preparations for the Commonwealth Games, when it was in power from 2009 to 2014.
"The Congress is making a desperate bid to make it an issue because it sees the whiff of opportunity," said Dr Sandeep Shastri, a political analyst.
"It is very clear that there are certain dimensions of the deal which are not clear and which could be in the zone of a controversy, especially the one involving Anil Ambani's company," he added.
"But I'm not sure if the Congress is equipped to make it an issue for a charge of corruption. It's becoming difficult for the opposition to pin it on the Prime Minister personally."
But political analyst Amulya Ganguly noted that the controversy has put pressure on the ruling party.
"It's all a game of bluff and bluster and it will continue. But it is putting BJP on the defensive."