New Delhi, Aug. 28 -- US Treasury yields have been rising, with the 30-year yield reaching around 5.24% this week, as investors demand higher returns to lend to the US government for longer periods. The move matters beyond the US because Treasury yields act as a benchmark for borrowing costs globally.

The US Treasury attempted to ease pressure on long-term borrowing costs this week by at least doubling the size of its bond buybacks from $2 billion to at least $4 billion per operation. Yields initially fell after the announcement but reversed course the following day, with the 30-year yield rising 0.06 percentage points to 5.24%.

The reversal highlighted the difficulty of using a relatively small market intervention to counter broader co...