US Fed chairman in appeal for action over 'unsustainable' debt burden

Though he offered no concrete proposals for fiscal reform, Bernanke flagged the rising cost of healthcare and social security programmes as key hurdles in refreshing his warnings on the United States' growing debt burden.

"In the absence of further policy actions, the federal budget appears set to remain on an unsustainable path," Bernanke told the 18-member National Commission on Fiscal Responsibility and Reform.

Bernanke said the nation's heavy debt load risked putting upward pressure on interest rates.

"Given the significant costs and risks associated with a rapidly rising federal debt, our nation should soon put in place a credible plan for reducing deficits to sustainable levels over time," Bernanke said.

His remarks come as investors around the world fret over a worsening debt crisis in Greece, which forced the country last week to ask for financial aid from fellow European Union nations and the International Monetary Fund.

Not all economists agree the US deficit is too large given the size of the economy and given the need for continued stimulus in the wake of the worst recession since the Great Depression.

"As long as private demand for new borrowing and spending is weak, then increased public borrowing will not cause sustained upward pressure on interest rates," argued economist Josh Bivens.