Yields on U.K. bonds have reached 5.81%, and German bonds are also paying 3.76%, versus 5.27% for a comparable U.S. bond. It's a big reason U.S. rates have been drifting higher.

U.S. Treasury bond sell-off coincided with the nonpartisan Congressional Budget Office's release of statistics that the national debt is about to cross $40 trillion.

Fears of a debt issuance glut swept across the US bond market this week, driving the 30-year yield to a nearly two-decade high.

Inflation, war and rising debt raise concerns among investors