WASHINGTON (Reuters) - U.S. President-elect Donald Trump's pick to be the next Treasury Secretary, Steve Mnuchin, told a Senate panel on Thursday he is concerned that a rule meant to block banks from speculating with their customers' money is hurting the financial system.

Part of the 2010 Dodd-Frank Wall Street reform law, the "Volcker Rule" prohibits banks from proprietary trading. But it is drying up liquidity, and the Treasury should look at its impact on the flow of cash through the financial system, Mnuchin said during the Senate Finance Committee hearing to confirm him for the secretary post.

Mnuchin added that he supports banking regulation, but he is concerned it is hurting small community banks and he would work as secretary to eliminate overlap in various regulators' rules.

(Reporting by Lisa Lambert; Editing by Chizu Nomiyama)