NEW YORK (CNNMoney) -- Treasury prices fell Tuesday, after Japan announced it will buy eurozone bonds to help prevent the spread of the region's debt crisis. The announcement reversed a three-day rise in bond prices. Treasury prices have been rising ever since reports on weekly unemployment claims and the December job market both came in weaker than expected last week. Then, over the weekend, jitters about Europe's debt crisis came back into the spotlight, as Portugal is under pressure to take a bailout. That uncertainty about the euro zone lent additional support to Treasury prices, sending yields -- which move in the opposite direction -- falling Monday. Since U.S. Treasuries are viewed as a low risk asset in times of uncertainty, their prices often rise when economic news disappoints. But when Japan said it would support the European debt market with a bond purchase early Tuesday, it sent bonds in the other direction. "Now that Japan has come in and said they're going to be a buyer, that has helped break the cycle of a string of bad news out of Europe," said Jim Vogel, head of agency debt research at FTN Financial. "That means that Treasury prices are a little bit freer to go back and forth today." The yield on the benchmark 10-year note ticked up to 3.31% from 3.29% on Monday. The yield on the 30-year bond rose to 4.49%, while the 5-year note was flat at 1.92% and the 2-year note was barely changed at 0.58%. Meanwhile, bond traders will be closely watching the first of three government debt auctions totaling $66 billion this week. Tuesday brings a $32 billion auction in three-year notes. A sale of $21 billion in 10-year notes follows on Wednesday and $13 billion in 30-year bonds are scheduled for auction Thursday.

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