The Treasury secretary asked for updates on how markets were functioning and inquired about any stresses in the system, according to one bank chief executive. Another bank C.E.O. was so unconcerned about the recent fall in stocks that he used his time with Mr. Mnuchin to discuss new capital requirements and how they could affect the bank’s balance sheet in the long term as the Fed continues selling government securities it amassed during the financial crisis, according to a person with knowledge of the discussion.

Policymakers who participated in the President’s Working Group call on Monday also described it as a routine meeting, with no market problems reported and nothing to warrant an official statement after the discussion. The call was described by a person familiar with the conversation as a “check-in” scheduled at the Treasury’s request for officials so they could plan for a prolonged government shutdown.

Negotiations to end the partial government shutdown have remained at an impasse since midnight Friday when funding lapsed for a number of federal agencies and nine departments, including the Treasury. Neither chamber is expected to reconvene until Thursday, with House lawmakers looking to the Senate Democrats and Mr. Trump to reach a compromise over border security funding.

The decision to convene the working group, which became known as the Plunge Protection Team during the 2008 financial crisis, struck some former officials as curious given that its duties have mostly been taken over by the Financial Stability Oversight Council. That body, which was created by the 2010 Dodd-Frank law, held a public meeting last week when it also published its annual report, which had little mention of market concerns.

“Now that the administration has chosen this extremely rare policy approach of verbal intervention in the stock market its credibility is at risk should markets settle lower,” said Michael O’Rourke, chief market strategist at JonesTrading.

Former Treasury officials said Mr. Mnuchin had probably amplified concerns about the markets by publicizing his efforts to calm them.

“I never heard anyone in any venue in the last two months voice any concerns about liquidity,” said Paul H. O’Neill, who served as Treasury secretary under President George W. Bush, noting that Mr. Mnuchin had injected more uncertainty into the calculations of investors.