By Aditya Kalra and Sumeet Chatterjee

NEW DELHI (Reuters) -Indian billionaire Gautam Adani has been indicted by U.S. prosecutors for his alleged role in a $265 million bribery scheme, plunging his conglomerate deep into crisis for the second time in two years.

The multiple counts of fraud levelled against Adani, who is one of the world's richest people, and seven other defendants, sent shares and bonds of Adani firms tumbling on Thursday. Adani Green Energy, the company at the centre of the allegations, also cancelled a $600 million bond sale.

Arrest warrants have been issued for Adani and his nephew Sagar Adani and prosecutors plan to hand those warrants to foreign law enforcement, court records show.

U.S. federal prosecutors said the defendants agreed to pay the bribes to Indian government officials to obtain contracts expected to yield $2 billion of profit over 20 years, and develop India's largest solar power plant project.

They also said the Adanis and another executive at Adani Green Energy's former CEO Vneet Jaain raised more than $3 billion in loans and bonds by hiding their corruption from lenders and investors.

The three were charged with securities fraud, securities fraud conspiracy and wire fraud conspiracy. The Adanis were also charged in a parallel U.S. Securities and Exchange Commission (SEC) civil case.

"Gautam and Sagar Adani were engaged in the bribery scheme during a September 2021 note offering by Adani Green that raised $750 million, including approximately $175 million from U.S. investors," the SEC said in a press statement.

"The SEC's complaint against Gautam and Sagar Adani charges them with violating the antifraud provisions of the federal securities laws. The complaint seeks permanent injunctions, civil penalties, and officer and director bars," it added.

The charges follow much turmoil for the Adani Group last year after short-seller Hindenburg Research issued a report that accused it of using offshore tax havens improperly - which the company has denied.

Shares in Adani Green Energy plunged 17% and stocks for many other firms in the conglomerate lost more than 10%. The group lost $28 billion in value in Thursday trade, putting its firms' combined market capitalisation at $141 billion. Before last year's Hindenburg report, the group's market value was $235 billion.

Adani dollar bonds slumped, with prices down between 3-5c on bonds for Adani Ports and Special Economic Zone.

"NUMERO UNO", "THE BIG MAN"

The unsealed criminal charges by the U.S. Attorney's Office for the Eastern District of New York showed some conspirators referred privately to Gautam Adani with the code names "Numero uno" and "the big man," while Sagar Adani allegedly used his cellphone to track specifics about the bribes.

Five other defendants were charged with conspiring to violate the Foreign Corrupt Practices Act, a U.S. anti-bribery law, and four were charged with conspiring to obstruct justice.

None of the defendants is in custody, a spokesperson for U.S. Attorney Breon Peace in Brooklyn said. Gautam Adani is believed to be in India.

Gautam Adani is worth $69.8 billion according to Forbes magazine, making him India's second-richest man after Mukesh Ambani. He is one of the few billionaires formally accused in the United States of criminal wrongdoing.

Shares in GQG Partners, an Australia-listed investment firm that is a major Adani backer, slid 20%, its largest one-day fall since it listed three years ago. It said in a statement that it was monitoring the charges.