The gap between U.S. bank deposits and loans is growing at the fastest pace in two years, providing lenders with more funds to buy bonds and temper the biggest sell-off in Treasuries since 2010.

As deposits increased 3.3 percent to $8.88 trillion in the two months ended July 31, business lending rose 0.7 percent to $7.11 trillion, Federal Reserve data show. The record gap of $1.77 trillion has expanded 15 percent since May, the biggest similar-period gain since July, 2010. Banks have already bought $136.4 billion in Treasury and government agency debt this year, more than double the $62.6 billion in all of 2011, pushing their holdings to an all-time high of $1.84 trillion.

Faced with a slowing U.S. economy, unemployment above 8 percent for more than three years and regulations forcing them to hold more and higher-quality assets, banks are lending at below pre-recession levels. The bond purchases help explain why even after rising this month, Treasury 10-year note rates are about half the 3.5 percent median forecast of 43 economists in a Bloomberg survey a year ago.