Adani Group chairman Gautam Adani has seen his net worth hit by a plunge firm's share price this week / © AFP
Shares in the business empire of Asia's richest man Gautam Adani sank again Friday after the conglomerate slammed a US investment firm that claimed it had committed "brazen" corporate fraud.
Hindenburg Research this week alleged in a report that Adani Group had used undisclosed related-party transactions and earnings manipulation to "maintain the appearance of financial health and solvency" of its listed business units.
Shares in flagship Adani Enterprises plunged six percent in opening trade on the Mumbai bourse, the first session after Thursday's Republic Day holiday, before recovering to two percent down.
Adani's sprawling interests range from Australian coal mines to India's biggest ports and the combined market cap of its seven listed companies exceeds $218 billion.
But Wednesday saw a major sell-off of Adani shares when trade resumed after the report's release, wiping $6 billion from its founder's net worth and knocking him down one place to fourth on Forbes' real-time global rich list.
Adani said Thursday it was the victim of a "maliciously mischievous" reputational attack by Hindenburg just as it was preparing for a major fundraising round.
Legal chief Jatin Jalundhwala said in a statement that the conglomerate was exploring its punitive action against the research advisory in US and Indian courts.
Hindenburg responded that Adani had ducked the issues its research had raised and instead resorted to "bluster and threats".
"If Adani is serious, it should also file suit in the US," the firm said in a statement. "We have a long list of documents we would demand in a legal discovery process."
Shares in Adani business units have soared as much as 2,000 percent in the past three years, adding more than $100 billion to its founder's net worth and vaulting him up the ranks of the world's richest people.
Adani -- who now has an estimated fortune of around $120 billion -- is considered a close supporter of Prime Minister Narendra Modi.
Hindenburg's report accused Adani Group of engaging in a "brazen stock manipulation and accounting fraud scheme over the course of decades".
It claimed Adani's elder brother Vinod managed "a vast labyrinth of offshore shell entities" in tax havens including Mauritius, Cyprus and several Caribbean islands.
The report said a pattern of "government leniency towards the group" stretching back decades had left investors, journalists, citizens and politicians unwilling to challenge the group's conduct "for fear of reprisal".
Its allegations come ahead of an ambitious $2.5 billion follow-on public offer -- India's biggest-ever -- due to open for bids on Friday and aimed at bolstering the business empire's balance sheet.