U.S. government debt prices were higher on Monday as investors eyed falling oil prices.
The yield on the benchmark 10-year Treasury notes, which moves inversely to price, was lower at 2.376 percent, while the yield on the 30-year Treasury bond was also lower at 2.969 percent.
U.S. Treasurys followed European bonds higher, as the 10-year German bund yield fell to 0.275 percent, while U.K. government bond yields also slipped amid talk of Britain drastically reworking trade ties with the European Union after Brexit.
There are no major economic data due Monday. However, Atlanta Federal Reserve President Dennis Lockhart said in a speech the central bank should step aside, as the economic crisis is "largely done." Lockhart is due to retire from his post in February.
Separately, Boston Fed President Eric Rosengren said the U.S. central bank should step up its pace of interest-rate increases from the once-a-year pattern it has pursued since 2015, warning of inflation risks if it does not. "I expect that appropriate monetary policy will need to normalize more quickly than over the past year," Rosengren said in prepared remarks.
In oil markets, U.S. crude settled at $51.96 a barrel, down 3.76 percent, as increased exports from Iran appeared to weaken the efforts by other oil producers to curtail global oversupply.
—Reuters contributed to this report.