NEW DELHI - A new anti-corruption party accused the son-in-law of India’s most powerful politician, Sonia Gandhi, of large-scale graft Friday at a news conference targeting the country’s famed ruling dynasty.

Social activist Arvind Kejriwal, who launched his as yet unnamed new party earlier in the week, accused Gandhi’s businessman son-in-law Robert Vadra of benefiting from murky deals in real estate linked to property group DLF.

“We want to know how his wealth grew from five million rupees ($90,000) to three billion in a span of three years?” he told the news conference in which he handed out papers he claimed were sourced from the registrar general’s office.

There was no immediate comment available from Vadra or from the registrar general’s office but a spokesman for the ruling Congress party Manish Tewari called the allegations “completely baseless”.

“There can be no case of corruption against Vadra,” Tewari said. “Members of the new party are indulging in petty politics and we are not interested in this kind of tactics.”

Kejriwal said every transaction made by Vadra’s companies were examined by independent chartered accountants to unearth the “fraud”.

“Everyone would like to know why was he given the houses and lands at throwaway prices? The nation must be informed,” he said.

Vadra is married to Sonia’s daughter Priyanka. Italian-born Sonia’s 42-year-old son Rahul is widely seen as being groomed for the role of prime minister.

Sonia Gandhi, president of India’s ruling Congress party, is widely seen as the country’s most powerful politician and the family’s privacy is fiercely guarded by party members.

The Nehru-Gandhi dynasty has ruled India for most of post-independence history, with three members of the family becoming prime minister.

Vadra calls himself an entrepreneur heading a small firm, Artex, which specialises in jewellery and handicraft exports.

He is also a self-confessed fitness freak who enjoys riding his motorbike and is frequently seen on New Delhi’s social circuit.

A spokesman for real estate firm DLF said the business relationship with Vadra was “completely transparent and was conducted to highest standards of ethics”.

The latest accusations come after Prime Minister Manmohan Singh’s Congress-led government has been rocked by a string of graft accusations, including allegations that officials pocketed millions of dollars when awarding tenders for telecoms and coal-mining ventures.