A widely watched section of the U.S. Treasury yield curve hit its deepest inversion on Monday since the high inflation era of Fed Chairman Paul Volcker, reflecting financial markets' concerns that an extended Federal Reserve rate hiking cycle will tip the United States into recession. The closely-watched spread between the 2-year and 10-year U.S. Treasury note yields hit the widest since 1981 at -109.50 in early trade, a deeper inversion than in March during the U.S. regional banking crisis.