"People are not willing to sell Treasuries," said Thanos Bardas, a managing director in Chicago at Neuberger Berman, which oversees about US$89 billion in fixed-income assets.
"The data in the US doesn't look as good," Bardas said.
"The labour market has lost momentum. There will be more upside left in Treasuries despite the low levels of rates."
Concern that the economy is losing momentum came when a Labour Department report showed American employers added fewer workers to payrolls last month than forecast and the jobless rate stayed at 8.2 per cent.
The International Monetary Fund will reduce its 3.5 per cent estimate for global growth this year on weakness in investment, jobs and manufacturing in Europe, the US, Brazil, India and China, managing director Christine Lagarde said.
Treasuries trail the Standard & Poor's 500 index of stocks, which has returned 9 per cent with reinvested dividends, while beating the 6 per cent loss posted by the Thomson Reuters/Jefferies CRB Index of raw materials.
"There is a reach for quality in the market," said Larry Milstein, managing director in New York of government and agency debt trading at RW Pressprich & Co.
The Fed under chairman Ben Bernanke bought US$2.3 trillion of Treasury and mortgage-related debt to stimulate the economy.
It decided last month to extend a policy known as Operation Twist where it sells short-term securities and uses the proceeds to buy longer-term debt.
- Bloomberg