Traders bought U.S. Treasury bonds, pushing the yield on the 10-year lower by 0.045-percentage point to 1.594%. 

In metals, gold gained $5.40, or 0.34%, to $1,597 a troy once. 

Spain said over the weekend that it plans on seeking up to $125 billion in aid from the 17-member eurozone to support its banks. There have been concerns for weeks that banks there that are laden with under-performing European sovereign debt and poorly-performing real estate loans could fail and potentially dramatically worsen that debt crisis. 

In a statement, eurozone leaders said that they are "willing to respond favourably" to such a request.  

However, the details remained murky, making many market participants very cautious. In particular, it remains unclear which rescue facility will be used to provide the loans. There is the temporary European Financial Stability Fund and the permanent European Stability Mechanism, both of which come with their own strings attached.