The largest US bank is siding with upstart market IEX Group in its effort to create a new stock exchange that pledges to be a haven for long-term investors.

Executives at JP Morgan Chase say regulators should approve IEX's bid to become an exchange, a move that would allow the newcomer to invade the ranks of established rivals such as the New York Stock Exchange and Nasdaq. The bank's endorsement illustrates how even the largest Wall Street banks have warmed to a competitor that once said the stock market was rigged and vowed to disrupt how shares are traded.