The JP Morgan Chase trader known as the "London whale" tried to alert others at the bank to mounting risks months before his bets ballooned into more than $6bn in losses, according to people familiar with emails reviewed by JP Morgan and a US Senate panel.

The apparent reservations of Bruno Iksil, who earned the nickname after making outsize wagers in debt markets, are among the details being examined by the Senate Permanent Subcommittee on Investigations, according to people familiar with the probe.