Treasury Secretary Steven Mnuchin looked to quash big-bank worries over plunging stock markets and reports that President Donald Trump might move on his Federal Reserve chief by assuring the financial community Sunday that market liquidity is in good shape.

Some market participants, however, questioned why Mnuchin answered a question that no one was asking. Even after recent market losses, a liquidity squeeze or fresh financial crisis hadn't been on the market's mind. Mnuchin's assertion of ample liquidity risked raising doubts.

Mnuchin tweeted late Sunday afternoon that he had called the chief executive officers of the nation's six largest banks and that those chiefs "confirmed they have ample liquidity available for lending to consumer, business markets, and all other market operations." Treasury also said Mnuchin would convene a call on Monday with the President's Working Group on financial markets.