U.S. Treasury Secretary Janet Yellen on Thursday urged Congress to raise the $31.4 trillion federal debt limit and avert an unprecedented default that would trigger a global economic downturn and risk undermining U.S. global economic leadership.

Yellen issued the latest in a series of increasingly stark warnings in remarks prepared for a press conference ahead of a meeting in Japan with her counterparts from the Group of Seven (G7) rich nations, as well as India, Indonesia and Brazil.

“A default would threaten the gains that we’ve worked so hard to make over the past few years in our pandemic recovery. And it would spark a global downturn that would set us back much further,” she said. “It would also risk undermining U.S. global economic leadership and raise questions about our ability to defend our national security interests.”

U.S. President Joe Biden on Wednesday said failure by Congress to act before Treasury runs out of money to pay the government’s bills -- something that could happen as early as June 1 — risked throwing the U.S. economy into a recession.

Yellen said Republican brinkmanship on the issue amounted to a “crisis of our own making” and that just the threat of a default could lead to a downgrade of the U.S. government’s credit rating, as occurred during a debt ceiling fight in 2011.

It could drive interest rates higher on mortgages, auto payments and credit cards, Yellen said, noting that rates were already spiking on debt due around June 1.

The US economy would suffer a “substantial” hit if Treasury was no longer able to issue debt, not to mention the impact on financial markets and institutions and consumer confidence, she said, calling the prospect “unthinkable.”

“All of these analyses show that we would fall into — if this lasted for any meaningful period of time -- a very substantial downturn,” she said.