The U.S. Securities and Exchange Commission (SEC) is investigating whether currency traders at the world's biggest banks distorted prices for options and exchange-traded funds (ETFs) by rigging benchmark foreign-exchange rates, according to two people with knowledge of the matter.

The SEC's inquiry adds to European and U.S. regulatory probes of possible manipulation in currency markets. The SEC's investigation is in the early stages, said the people, who asked not to be named because the matter isn't public. The Commodity Futures Trading Commission (CFTC), which regulates foreign-exchange derivatives, is also investigating possible manipulation, another person said.

Authorities from London to New York have contacted at least a dozen banks as they investigate allegations, first reported by Bloomberg News in June, that dealers said they shared information about client orders to manipulate benchmark spot rates for currencies. Derivatives such as options account for more than half of the $5.3 trillion-a-day foreign-exchange market; the rest is made up of spot transactions.