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.

The Securities and Exchange Board of India took action against Jane Street Capital. Operations in Mumbai were halted. Assets worth over half a billion dollars were seized. Analysts predict a drop in derivative market volumes.

India’s regulator has temporarily barred Jane Street from accessing the local securities market, dealing a severe hit to the US firm that allegedly made $4.3 billion in trading gains in the South Asian nation in more than two years.