The U.S. Treasury said Wednesday it will buy back more of its longer-term bonds to curb a sharp increase in borrowing costs. The current maximum size of $2 billion per operation will be at least $4 billion per operation, targeting longer-dated nominal coupon securities with maturities 10 years or longer. The change takes effect Sept. 9 through Nov. 4, with an update at the next quarterly refunding on Nov. 4.

The announcement intensified an overnight decline in Treasury yields, which have reached multiyear highs. The 30-year yield settled at 5.31% Monday, the highest since June 2007, days after the Treasury paid the highest 30-year auction yield in 25 years at 5.22%.

However, the effort may not provide long-term stability in bond markets, said Ross Pamphilon, fixed income head at asset management firm Impax.