ZURICH, March 31 (Reuters) - Switzerland's competition watchdog said on Monday it had opened an investigation into several Swiss, British and American banks over possible collusion to manipulate foreign exchange rates.

WEKO said it is investigating UBS, Credit Suisse , Zuercher Kantonal Bank, Julius Baer, JP Morgan, Citigroup, Barclays and Royal Bank of Scotland.

(Reporting by Caroline Copley; Editing by Matt Driskill)