JPMorgan said it has logged $1.5 billion of losses so far this quarter on mortgage-linked assets, reflecting continuing turmoil in credit markets, according to Reuters.

Chief executive Jamie Dimon has kept JPMorgan profitable even as rivals such as Citi, Merrill Lynch and UBS posted a series of quarterly losses. The US bank revealed the losses in a regulatory filing.

JPMorgan said trading conditions have "substantially deteriorated" in the third quarter, and mortgage-backed securities and loans have weakened.

The New York-based bank, which covers activities including wealth management, also has substantial exposure to credit cards and other consumer debt that looks increasingly vulnerable as growth in the US economy slows.

JPMorgan is under pressure to write down mortgage assets, in part because of Merrill's decision to sell $30.6 billion of repackaged debt to a private equity fund at 22 cents on the dollar.

As of 30 June, JPMorgan held $19.5 billion of prime and Alt-A mortgage exposure, $1.9 billion of subprime mortgage exposure, and $11.6 billion of commercial mortgage-backed securities exposure, the regulatory filing showed.