JP Morgan Chase has taken $2bn in trading losses in the past six weeks and could face an additional $1bn in second quarter losses due to market volatility, chief executive Jamie Dimon said in a hastily arranged conference call after US markets closed.

The losses stemmed from derivatives bets gone wrong in the bank's chief investment office, which manages risk for the New York company. The Wall Street Journal reported last month that large bets - by a London-based trader named Bruno Michel Iksil - being made in that office had roiled a sector of the debt markets.