High anxiety over the public debt problem in Europe and wild swings in global stock markets due to economic worries also have rekindled safe-haven bids for ultra short-dated US government securities.

On Monday, indirect bidders bought 30.5 percent of the $29 billion in three-month bills offered by the US Treasury Department. That was was up sharply from prior week's 7.6 percent, according to Treasury data.

At the same time, indirect bidders purchased 35.8 percent of the $27 billion in new six-month bill supply That was nearly double the amount they bought last week.

Copyright Reuters, 2011