WASHINGTON (AP) -- Interest rates on short-term Treasury bills rose in Monday's auction with rates on six-month bills rising to the highest level in three weeks.

The Treasury Department auctioned $29 billion in three-month bills at a discount rate of 0.045 percent, up from 0.040 percent last week. Another $24 billion in six-month bills was auctioned at a discount rate of 0.080 percent, up from 0.075 percent last week.

The three-month rate was the highest since these bills averaged 0.050 percent on April 29. The six-month rate was the highest since these bills averaged 0.085 percent on April 22.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,998.86 while a six-month bill sold for $9,995.96. That would equal an annualized rate of 0.046 percent for the three-month bills and 0.081 percent for the six-month bills.

Separately the Federal Reserve said Monday that the average yield for one-year Treasury bills, a popular index for making changes in adjustable rate mortgages, was unchanged at 0.11 percent last week, the same as the previous week.