The last time bonds were the only assets with positive returns was January 2008. Government debt globally returned 0.7 percent in April, a Bank of America Merrill Lynch index showed.

U.S. Treasuries, perceived as the safest of assets, gained 1.5 percent, led by a 4.8 percent return for 30-year bonds in their best month since September. Yields on Treasuries due in 10 years, which were 1.91 percent as of 7:55 a.m. in London, are forecast to climb to 2.26 percent in June 2012, according to the median estimate of 78 economists surveyed by Bloomberg.

Portugal's bonds were the best performers among the 26 sovereign markets tracked by Bloomberg and the European Federation of Financial Analysts Societies, jumping 6.3 percent. Debt of Italy and Spain were the worst, losing more than 2 percent each.

Corporate Bonds

Investment-grade corporate securities gained 0.8 percent. High-yield, high-risk, or junk, bonds returned 0.7 percent. Speculative-grade debt is rated below Baa3 by Moody's Investors Service and less than BBB- at S&P.

The U.S. Dollar Index, which Intercontinental Exchange Inc. uses to track the currency against the euro, yen, pound, Swiss franc, Canada dollar and Swedish krona, fell to 78.78 from 79 at the end of March.

The index peaked last month at 80.177 on April 5, a day before the U.S. Labor Department said employers created 120,000 jobs in March. The median estimate of economists surveyed by Bloomberg was for an increase of 205,000.

Federal Reserve Chairman Ben S. Bernanke said last week the central bank stands ready to add to its stimulus measures if necessary, which for many investors means the printing of more dollars to buy bonds.

After his comments, a U.S. government report showed the economy expanded at a 2.2 percent annual pace in the first quarter, down from 3 percent in the final three months of 2011. The median forecast of economists surveyed by Bloomberg News called for a 2.5 percent rise.

'Cost-Reduction Mode'

"I'm going to question to whether consumer spending is sustainable over the long term," said Calvert's Duch, who favors intermediate-maturity Treasuries. "Employers are still in cost-reduction mode. Employees are feeling that they don't have the leverage, and wages are going to remain static for a long period of time."