India has barred one of the world's largest quant trading firms, Jane Street, from accessing its securities market after an investigation found it made "unlawful gains", taking the most stringent action ever against a foreign trading firm.

India has temporarily barred Jane Street Group LLC from accessing the local securities market for alleged index manipulation, dealing a severe hit to the US firm that made $4.3 billion in trading gains there in more than two years.

Portfolio manager Mayank Bansal exposes options trading fraud, prompting SEBI to ban U.S. firm and seize ₹4,843 crore. Interview insights.