The U.S. Treasury Department's auction of 10-year bonds Wednesday showed strong demand, with its high yield rising to its highest level in 19 years, following the earlier announcement of an increased buyback operation for longer-run maturities.

The Treasury sold $39 billion of bonds at its monthly auction, with a high yield of 4.834%. That was the highest high yield for the U.S. 10-year auction since Aug. 8, 2007, when it was 4.855%.

Following the auction, the U.S. 10-year yield hovered around 4.84%.

The bid-to-cover ratio, a measure of investor demand, was 2.71, topping the prior six-month average of 2.50.

Earlier Wednesday, the Treasury raised the size of its planned buyback operation for bonds maturing in 10 to 20 years to $6 billion, triple the typical amount. Yields rose following the release of that plan which suggested the increased size was within investors's expectations.