WASHINGTON D.C.: The U.S. Treasury is doubling the size of planned buybacks of longer-dated government debt after a weeks-long rise in yields that had unsettled global investors.

The Treasury said August 19 that buybacks of 10- to 30-year securities would increase to at least US$4 billion per operation from the previously planned $2 billion. The increase will apply to the 10- to 20-year and 20- to 30-year sectors from September 9 through November 4.

The announcement came a day after a major bond selloff pushed the 30-year Treasury yield to its highest level since 2007, amid worries about an imminent escalation in the U.S.-Israeli war with Iran and concerns over the U.S. fiscal outlook as total public debt approaches $40 trillion.

The 30-year yield reached a 19-year high of 5.34 percent on Wednesday before easing. Following the Treasury announcement on Thursday, it fell to 5.187 percent, marking its largest daily decline since late June. The benchmark 10-year Treasury yield was also lower, down 6 basis points at 4.65 percent.

"This increase in buyback operation sizes reflects Treasury's desire to provide greater liquidity support in longer-dated nominal sectors where there is consistently strong sponsorship from market participants, as evidenced by the significant volume of high-quality offers Treasury routinely receives in longer-dated buyback operations," the Treasury said.

Market analysts said the action reflected sensitivity to debt-market pressures that could increase government borrowing costs, keep mortgage rates elevated and risk broader financial-market disruptions.

"I think they fear the pain of five percent or higher yields on the long end, not only because it raises the interest rate costs for the government but also for the private sector," said Rene Albrecht, senior analyst at DZ Bank in Germany. "It's only three months until the midterm elections."

"They have had to reach into the toolkit to get a hand on the recent rise in yields," Albrecht added.

The increase marked the second time this month Treasury Secretary Scott Bessent has intervened to counter market moves, after joining Japan in an August 1 currency-market intervention aimed at reversing the yen's slide to recent 40-year lows against the dollar.

Evercore ISI analysts described Bessent as an "activist Treasury secretary" but questioned whether the increased buybacks would have a lasting effect.

"The operation changes almost nothing in terms of the fundamentals, in particular the unchanged need to finance the tidal wave of hyperscaler debt in addition to very large government deficits. The increased size of the operations is modest relative to the flows in the Treasury market," Evercore ISI said.

The $2 billion increase is small compared with the $32.2 trillion Treasury debt market as of August 17 and about $5.5 trillion of outstanding 20- and 30-year bonds as of July 31.

Overall public debt, including intergovernmental holdings, stood at $39.99 trillion on August 17.

The Treasury has conducted scheduled purchases of older securities for the past two years to provide liquidity for so-called off-the-run debt. Earlier this month, it said it would repurchase up to $69 billion of Treasuries across all maturities between August 6 and November 5.

With the larger operations, scheduled buybacks will provide at least an additional $14 billion of liquidity support, bringing maximum repurchases during the period to $83 billion.