The bank had registered a net profit of Rs 110.52 crore in the July-September quarter of previous fiscal.
The bank's provisions to cover bad assets and contingencies rose substantially to Rs 453.68 crore for the quarter under review, from Rs 128.33 crore parked in the corresponding period last fiscal.
"Provisions (other than tax) and contingencies include depreciation of Rs 252.39 crore on account of diminution in net asset value (NAV) of investments in security receipts on the basis of NAV declared by Asset Reconstruction Company as at September 30, 2017," the bank said in a regulatory filing.
"Based on preliminary investigation, the bank has filed an FIR and has initiated suitable recovery or other legal proceedings. The loss will be accounted in accordance with RBI guideline over a period of four quarters commencing from the quarter ended September 2017," it added.
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Total income of the bank, however, rose to Rs 1,816.67 crore during September quarter of the current fiscal, as against Rs 1,596.08 crore in the year-ago period, the bank said.
Net NPAs, as a percentage of net advances, stood at 2.57 per cent as on September-end this year, down from 2.77 per cent in the year-ago period, bank's profit and loss balance- sheet showed.
Shares of South Indian Bank tumbled by 6.55 per cent to Rs 29.95 per unit on BSE.