Gautam Adani, one of the world’s richest men, has been indicted in New York over an alleged multibillion-dollar scheme to pay $250m in bribes and conceal it from US investors.

Prosecutors charged the chair of the Indian conglomerate Adani Group and two other executives of a renewable energy company with securities fraud and conspiring to commit securities and wire fraud.

The US attorney’s office in Brooklyn accused the executives of agreeing to pay hundreds of millions of dollars’ worth of bribes to Indian government officials between 2020 and 2024, in an attempt to obtain solar energy supply contracts expected to make $2bn in profits over 20 years.

Separately, the Securities and Exchange Commission, the US’s top markets watchdog, charged Adani, 62, and two other executives over conduct it said had arisen out of a “massive bribery scheme” that involved $175m from US investors.

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

The Adani group said the allegations were baseless. In a statement, they said: “As stated by the US Department of Justice itself, ‘the charges in the indictment are allegations and the defendants are presumed innocent unless and until proven guilty’. All possible legal recourse will be sought.”

In the aftermath of the allegations, shares in Adani Green Energy plunged 17% and stocks for many other firms in the conglomerate lost more than 10%. The group lost $28bn in value in Thursday’s trade. Adani Green Energy, the company at the centre of the allegations, also cancelled a $600m bond sale.

The falls were the largest since the Adani Group came under a short-seller attack in February 2023, after allegations of “brazen” stock manipulation, accounting fraud and money laundering were published by the short seller investment firm Hindenburg Research last year.

Adani denied the Hindenburg claims, which it dismissed as a “malicious” mix of “selective misinformation and stale, baseless and discredited allegations”.

Breon Peace, the US attorney for the eastern district of New York, said the defendants “orchestrated an elaborate scheme” to bribe India’s officials to secure contracts and lied about the scheme while raising funds.

Lisa Miller, the deputy assistant attorney general, said: “This indictment alleges schemes to pay over $250m in bribes to Indian government officials, to lie to investors and banks to raise billions of dollars, and to obstruct justice.

“These offenses were allegedly committed by senior executives and directors to obtain and finance massive state energy supply contracts through corruption and fraud at the expense of US investors.”

Gautam Adani is the 18th richest person in the world, according to Bloomberg, with a personal fortune of $85bn.

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Prosecutors alleged that, on several occasions, Adani personally met with an Indian government official to advance the bribery scheme.

The executives are accused of having frequently discussed efforts to further the scheme, including via a messaging app. Sagar Adani tracked “specific details of the bribes offered and promised to government officials” on his phone, according to prosecutors.

The allegations provoked a political firestorm in India. The Indian prime minister, Narendra Modi, has been accused repeatedly by political opponents and critics of a close and corrupt relationship with Adani and of protecting him from investigation or arrest over mounting allegations of corrupt practices. The Adani group denies it has benefited from any political patronage by the Modi government.

At a press conference, Rahul Gandhi, the most prominent face of India’s opposition, questioned why Adani had not been arrested and accused Modi of protecting him.

“It’s pretty clear and established in America that Mr Adani has broken both American law and Indian law,” said Gandhi. “I’m wondering why Mr Adani is still running around a free man in this country … it’s a vindication of what we’ve been saying. The prime minister is protecting Mr Adani and the prime minister is involved in corruption with Mr Adani.”

Gandhi said he would be raising the issue when parliament meets next week. “Adani has hijacked India … the country is in Adani’s grip,’ he said.