French regulator AMF said on Thursday it had opened an investigation into ratings agency Standard & Poor's erroneous release earlier in the day of a message suggesting France's credit ratings had been downgraded.

The markets watchdog announced the probe after French Finance Minister Francois Baroin earlier asked regulators to investigate the causes and consequences of the error.

The AMF also said it had contacted the European Securities and Markets Authority (ESMA) about the matter.

(Reporting By Christian Plumb)