WASHINGTON (AP) — Interest rates on short-term Treasury bills rose in Monday's auction to their highest levels in nine years.

The Treasury Department auctioned $51 billion in three-month bills at a discount rate of 1.645 percent, up from 1.630 percent last week. Another $45 billion in six-month bills was auctioned at a discount rate of 1.830 percent, up from 1.820 percent last week.

The three-month rate was the highest since those bills averaged 1.690 percent on Sept. 8, 2008. The six-month rate was the highest since those bills averaged 1.900 percent on Sept. 8, 2008.

The discount rates reflect that the bills sell for less than face value. For a $10,000 bill, the three-month price was $9,958.42 while a six-month bill sold for $9,907.48. That would equal an annualized rate of 1.675 percent for the three-month bills and 1.873 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, edged up to 2.02 percent on Friday, compared to 2.01 percent on Feb. 20.