The benchmark 10-year yield was down 5.4 basis points at 1.5903%.
Analysts pointed to a combination of factors driving trading including economic uncertainties tied to the coronavirus epidemic in China and a fall in German industrial output.
Those developments offset a Labor Department report on Friday showing US job growth accelerated in January, with nonfarm payrolls rising by 225,000 jobs.
The figures indicated the economy will probably continue to grow modestly despite a deepening slump in business investment.
"Weak European data, the coronavirus and contained inflation are outweighing the strong jobs report," said William Zox, chief investment officer for fixed income at Diamond Hill Capital Management.
Ordinarily the report would have pushed up yields, he said. But currently, Zox said, "the global picture is dominating" investors' attention.
The coronavirus death toll in mainland China reached 637 on Friday, with a total of 31,211 cases, WHO chief Tedros Adhanom Ghebreyesus said in Geneva, warning of a worldwide shortage of gowns, masks and other protective equipment.
"For the last two days there had been fewer reported infections in China, which is good news, but we caution against reading too much into that," he told the WHO executive board.
German industrial output suffered its biggest fall in December since the recession-hit year of 2009, a shock drop highlighting the weakness in manufacturing that risks dragging Europe's largest economy into contraction again.
Euro zone bond yields also fell as risk appetite dwindled on Friday and investors moved into safe-haven assets.
Economists polled by Reuters had forecast U..S. payrolls would rise by 160,000 jobs in January. Unseasonably mild temperatures boosting hiring in weather-sensitive sectors, according to the Labor Department report, which also showed the economy created 514,000 fewer jobs between April 2018 and March 2019 than originally estimated.
The two-year US Treasury yield, which typically moves in step with interest rate expectations, was down 2.8 basis points at 1.4192% in morning trading.