Merrill Lynch has been fined $13.5m (€10.1m) by US state regulators and the New York Stock Exchange for failing to supervise a group of its brokers who engaged in improper market timing of mutual funds.

The NYSE said in a statement that the brokers in Merrill Lynch's Fort Lee, New Jersey, office made more than 3,700 short-term mutual fund transactions on behalf of one hedge fund client at the bank. Merrill Lynch has fired the brokers involved.