Standard Chartered has had a hard time in South Korea since buying First Bank in 2005 for £2.1bn, its largest ever acquisition.
It had a long dispute with staff and the profitability for all banks there has been hit by tougher regulations.
Bad debts have also risen after an overhaul of personal debt restructuring processes, allowing more forgiveness on long-term loans.
The UK-listed bank, which makes more than 90 per cent of its profit in Asia, Africa and the Middle East, said excluding its Korean woes it would still meet consensus forecasts for a full-year operating profit of £5.1bn, up 15 per cent from last year.
Like larger rival HSBC, Standard Chartered has seen a slowdown in emerging markets, which has dented its stock price in recent months and tempered growth expectations.
Revenues have risen by an average 15 per cent a year over the last decade, slowing to eight per cent last year. The bank expects to fall short of its 10 per cent target again this year.
Standard Chartered reported a pretax profit of £2.1bn for the six months to the end of June, down from £2.5bn a year ago due to the writedown in Korea.
The bank had flagged a possible writedown in June. It posted a £560m pre-tax loss in Korea for the first half, after a two-thirds jump in loan losses and provisions for souring debt.
Chief executive Peter Sands said the bank would accelerate the restructuring of the business, including the sale of some assets.
“We cannot escape the realities of the Korean context, but we are determined to improve productivity,” he said.