NEW DELHI (AP) — Embattled Indian billionaire Gautam Adani called off his flagship company's $2.5 billion share share late Wednesday after a tumultuous week saw his conglomerate shed tens of billions of dollars in market value after claims of fraud from a U.S.-based short-selling firm.

Citing a volatile market and an unprecedented situation, the Adani Group said in a statement it decided not to go ahead with its share sale — which was preliminarily sold out as of Tuesday — and will return the proceeds from the offering.

Adani-related shares plunged in recent days after Hindenburg Research, a financial research firm with a track record of sending the stock prices of its targets tumbling, accused the group of "brazen" stock market manipulation and accounting fraud, among other financial abuses.

By the time trading closed Wednesday, Adani Enterprises was down by a whopping 28% — a day after its share sale drew nearly 51 million bids, exceeding the 45.5 million that was offered to the public. Stock in six of Adani's other listed companies also sunk between 2% and 19%.

"The market has been unprecedented and our stock price has fluctuated over the course of the day. Given these extraordinary circumstances, the Company's board felt that going ahead with the issue would not be morally correct," Adani said in his first remarks since the controversy.

He added that the group acted to protect its investors and insulate them from any financial losses.

The share sale and its success were seen as a crucial test of investor confidence in Adani. The stock losses on Wednesday cost Adani his title as the richest man in Asia and in India, as his fortune plummeted to $72 billion, according to Bloomberg. Prior to the Hindenburg report, his net worth at around $120 billion made him the world's third-richest man.

Hindenburg, which said it was betting against the Adani Group, accused it of "pulling the largest con in corporate history." It said it judged the seven key Adani listed companies to have an "85% downside, purely on a fundamental basis owing to sky-high valuations."

The firm said its report followed a two-year investigation. Most of the allegations involved concerns about the group's debt levels, activities of top executives, use of offshore shell companies to artificially boost share prices and past investigations into fraud. It listed 88 questions for the group to answer.

On Sunday, the Adani Group dismissed Hindenburg's allegations and issued a 413-page report that rejected its questions, saying none were "based on independent or journalistic fact finding." Adani's response included documents and data tables and said the group has made all necessary regulatory disclosures and abided by local laws.

Hindenburg responded by saying Adani had answered only 26 of its 88 questions and failed to address many of the issues it raised.

In his statement Wednesday, Adani said the decision to scrap the share offering would not "have any impact on our existing operations and future plans," adding that the group's balance sheet was "very healthy" with strong cashflows and secure assets. "Once the market stabilizes, we will review our capital market strategy," he said.

Adani made a vast fortune mining coal as energy-hungry India grew swiftly after its economy was liberalized in the 1990s. The market value of his companies has soared in recent years. Adani companies operate airports in major cities, build roads, generate electricity, manufacture defense equipment, develop agricultural drones, sell cooking oil and run a media outlet.