Jan 21 (Reuters) - Private equity firm KKR & Co LP refunded money to investors in some of its buyout funds after U.S. regulators found it overcharged them, the Wall Street Journal reported on Wednesday, citing a pension-fund document.

The precise amount of the refunds could not be determined, but one set of refunds could be less than $10 million, while the other may have been similar in size or smaller, the Journal reported. (http://on.wsj.com/1zxrwJ6)

KKR's decision came after the Securities and Exchange Commission (SEC) found the firm charged investors wrongly for some expenses and failed to notify them properly of certain fees it collected, the WSJ report added.

The SEC and KKR could not immediately be reached for comment.

(Reporting by Sai Sachin R in Bengaluru; editing by Andrew Hay)