An Indian conglomerate owned by Asia's richest man Gautam Adani said Thursday it was exploring legal action against a US investment firm that accused it of "brazen" corporate fraud.

Hindenburg Research this week alleged 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.

Wednesday saw a major sell-off of Adani shares, wiping $6 billion from the net worth of its 60-year-old founder and knocking him down one place to fourth on Forbes' real-time global rich list.

Adani Group hit back on Thursday against Hindenburg's "maliciously mischievous" report and said it was the victim of a reckless reputational attack just as it was preparing for a major fundraising round.

"The volatility in Indian stock markets created by the report is of great concern and has led to unwanted anguish for Indian citizens," Adani legal chief Jatin Jalundhwala said in a statement.

Hindenburg's announcement that it had taken a short position in the group's companies was proof that the company had a vested interest in driving down share prices through the release of its report, he added.

"We are evaluating the relevant provisions under US and Indian laws for remedial and punitive action."

Adani's sprawling business empire has interests ranging from Australian coal mines to India's biggest ports and the combined market cap of its seven listed companies exceeds $218 billion.

Shares in its business units have soared up to 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 -- now with an estimated fortune of around $120 billion -- is considered a close supporter of Prime Minister Narendra Modi.

- 'Fear of reprisal' -


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.

Shares in flagship Adani Enterprises fell as much as three percent on Wednesday, before recovering to trade 1.07 percent lower at the close in Mumbai.

Indian markets were closed Thursday for India's national Republic Day holiday.