India's Securities and Exchange Board (SEBI) has temporarily barred U.S.-based quantitative trading firm Jane Street Group from accessing the country's securities market amid an ongoing investigation into alleged market manipulation. SEBI's interim order accuses Jane Street of manipulating stock index derivatives, particularly Bank Nifty and Nifty 50 options, through expiry-day trades that generated unlawful gains estimated at approximately Rs 4,843 crore (around $570 million). The regulator has directed banks to freeze Jane Street's accounts and impound these alleged illicit profits. Jane Street reportedly earned over Rs 36,671 crore ($4.3 billion) in net revenue from equity derivatives trading in India over the past two years. SEBI's probe has identified strategies involving manipulation of index closing prices on expiry days, which distorted market conditions and raised concerns among other algorithmic trading firms. The regulator is expanding its investigation to include other indices and exchanges, with potential further enforcement actions anticipated. Jane Street has denied the allegations, characterizing the charges as inflammatory and asserting that its trading practices constitute basic index arbitrage. The ban marks one of the most stringent actions taken by Indian authorities against a foreign trading firm and has raised concerns about liquidity and trading volumes in India's derivatives market. Market participants and brokers are monitoring the situation closely, given Jane Street's significant presence and influence in the Indian financial markets.