Fed chairman Ben Bernanke stepped up his warnings Tuesday over the looming “fiscal cliff,” saying its mandatory tax hikes and spending cuts posed a “substantial threat” to US economic recovery.

With President Barack Obama’s administration and Congress locked in crunch talks on avoiding the cliff and slashing the budget deficit, Bernanke said rising cuts to federal spending were already holding back growth.

“Congress and the administration will need to protect the economy from the full brunt of the severe fiscal tightening at the beginning of next year that is built into current law — the so-called fiscal cliff,” the US central bank chief said in a speech in New York.

“The realization of all of the automatic tax increases and spending cuts that make up the fiscal cliff, absent offsetting changes, would pose a substantial threat to the recovery,” he said, according to the prepared text.