US banking giant JPMorgan has revealed a surprise trading loss of $2bn (£1.2bn) on complex investments made by its traders.

Overall, after accounting for other gains, losses at its chief investment office are estimated to come in at $800m in the second quarter.

The loss could be as big as $1bn, chief executive Jamie Dimon said in an unscheduled conference call.

JPMorgan shares fell 6% after-hours, with other bank stocks following.

Goldman Sachs, Citigroup and Bank of America also suffered heavy losses in electronic trading after the market close.

The strategy taken at its chief investment office had been "riskier, more volatile and less effective" than previously believed, Mr Dimon said.

"There were many errors, sloppiness and bad judgement. These were egregious mistakes.

"They were self-inflicted and this is not how we want to run a business."

http://www.bbc.co.uk/news/business-18030022