"If the conditions are right, then I would anticipate we'll take advantage of long-term borrowing and execute on that," Mnuchin told Bloomberg in an interview.

Mnuchin said his renewed interest in 50- or 100-year bonds was unrelated to the drop in yields on shorter-term US debt,  Bloomberg reported.

Currently, the 30-year bond is the longest-dated US Treasury bond.

Earlier this month, the Treasury Department asked for feedback from market participants about the possibility of selling ultra-long bonds. The department posed a similar inquiry in 2017.

US Treasury debt yields fell on Wednesday, with 30-year yields setting all-time lows, as fears about a recession and US-China trade tensions stoked unrelenting demand for low-risk government debt.

Inversion is spreading across the US yield curve, where short-dated yields are running above long-dated ones, which has also unsettled investors as yield curve inversion often precedes a recession.