US Treasury Secretary Janet Yellen has launched a new call to Congress to raise the federal debt ceiling, according to her that a US debt default would trigger a major financial crisis.

The Secretary said that the crisis triggered by a default would increase the economic problems caused by the pandemic, and would drive the US into recession.

On another occasion, Yellen said a default could occur in October, when the Treasury depletes its cash reserves and borrowing capacity.

Republicans are refusing to support an increase in the debt ceiling, and argue that Democrats intend to raise the lending limit to fund trillions of dollars in spending on the "Democrats' wish list."