The U.S. dollar fell 0.7% on Aug. 19 to its weakest level since mid-May after the U.S. Treasury unexpectedly expanded long-term Treasury buybacks, supporting a rebound in the bond market. The ICE Dollar Index ended at 98.922, while the Bloomberg Dollar Spot Index also declined 0.7% and fell against all 10 major trading-partner currencies, including the euro, yen and South Korean won. The dollar dropped to 1,385.40 won in Seoul’s after-hours foreign-exchange market, its lowest level in about 12 months, while the yen strengthened as much as 0.9% to 158.17 per dollar. The Treasury said it would buy older long-dated bonds that had become difficult to trade after sharp price declines and expand long-bond buybacks to provide liquidity and manage government debt. The announcement pushed the 30-year Treasury yield down about 8 basis points, easing market stress but adding pressure to the dollar. Expectations that the Federal Reserve is unlikely to begin raising interest rates before December also weighed on the currency. The Treasury’s action came after concerns over surging federal debt, the war with Iran, inflation and increased corporate borrowing linked to artificial-intelligence investment drove a selloff in long-term bonds and lifted the 30-year yield to its highest level since 2007.