U.S. Treasury Secretary Janet Yellen on Monday said she saw no signs the U.S. economy is in a downturn but warned that failure by Congress to pass legislation to keep the government running risked slowing momentum in the economy.

"I don't see any signs that the economy is at risk of a downturn," Yellen told CNBC, noting that the U.S. labor market also remained strong and inflation was coming down.

"There's absolutely no reason for a shutdown," she said. "Creating ... a situation that could cause a loss of momentum is something we don't need as a risk at this point."

(Reporting by Andrea Shalal and Doina Chiacu; Editing by Mark Porter)