A JP Morgan Chase executive encouraged the trader known as the "London whale" to boost valuations on some trades, said a person who reviewed communications emerging from the bank's internal probe of recent trading losses.

After reviewing emails and voice-mail messages, the bank has concluded that Bruno Iksil, the JP Morgan trader nicknamed for the large positions he took in the credit markets, was urged by his boss to put higher values on some positions than they might have fetched in the open market at the time, people familiar with the probe said.