WASHINGTON (AP) – Interest rates on short-term Treasury securities rose in Monday’s auction.

The Treasury Department sold $17 billion in three-month bills at a discount rate of 0.920 percent, up from 0.905 percent last week. An additional $17 billion was sold in six-month bills at a rate of 1.015 percent, up from 0.985 percent.

The three-month rate was the highest since Sept. 29, when the bills sold for 0.935 percent. The six-month rate was the highest since Sept. 2, when the rate was 1.040 percent.

The new discount rates understate the actual return to investors – 0.939 percent for three-month bills with a $10,000 bill selling for $9,976.70 and 1.037 percent for a six-month bill selling for $9,948.70.

In a separate report, the Federal Reserve said Monday that the average yield for one-year constant maturity Treasury bills, the most popular index for making changes in adjustable rate mortgages, rose to 1.29 percent last week from 1.20 percent the previous week.