This photo taken on Wednesday in New York shows the US national debt surpassing $40 trillion. ZHANG FENGGUO/XINHUA

The United States Treasury Department said on Wednesday that total US government debt had surpassed $40 trillion, while announcing plans to at least double the maximum size of its liquidity-support buyback operations for longer-dated Treasury securities from $2 billion to at least $4 billion per operation.

Total outstanding public debt stood at $40.05 trillion at the close of business on Tuesday, according to Treasury data, surpassing an earlier Congressional Budget Office forecast that total federal borrowing would reach $39.4 trillion by the end of fiscal 2026.

The Treasury said the larger buybacks, covering the 10- to 20-year and 20- to 30-year sectors, will run from Sept 9 through Nov 4. The move is aimed at easing liquidity pressures in the long-term bond market, but does not address underlying structural challenges, including the persistent fiscal deficit and growing national debt, experts said.

US Treasury yields rose on Tuesday despite a previously scheduled $2 billion buyback of 20- and 30-year bonds. The 30-year Treasury yield briefly climbed to 5.34 percent, its highest level since 2007, before retreating.