The debt was also supported as the Federal Reserve planned to make two bond buybacks, totaling as much as $10 billion, in the second-to-last week of its quantitative easing program that is scheduled to end this month.

Euro zone ministers said Greece had to approve stricter austerity measures before a final decision is made on extending a further 12 billion euros in loans.

"The finance ministers have set a time frame now. The question is will there be any great surprise," said Tom Tucci, head of government bond trading at RBC Capital Markets in New York.

Treasuries have benefited from uncertainty in the euro zone, while weakening US economic data has also led investors to reduce expectations of monetary tightening.

Investors are now likely waiting on further clarity from Europe, or on the state of the US economy, before taking on new risk, said Tucci.

"People don't want to be making investment decisions with so much uncertainty surrounding the marketplace," he said. "Yields would fall further if people thought there was a significant shock coming to the financial system, or if the economic conditions in the US are going to continue to decline."

Benchmark 10-year notes rose 6/32 in price on Monday to yield 2.92 percent, down from 2.94 percent late on Friday. The debt has strong technical resistance at 2.88 percent, a the lowest level since the beginning of December and a level the notes tested last week.

Five-year notes also increased 4/32 in price to yield 1.51 percent, down from 1.53 percent on Friday and 30-year bonds rose 17/32 in price to yield 4.17 percent, down from 4.21 percent.

Fed buying through the end of June is likely to help support yields.

The central bank on Monday will buy $4 billion to $5 billion in Treasuries due from 2013 to 2015 and an additional $4 billion to $5 billion in debt due between 2018 and 2021.

The most liquid parts of the bond market could also be boosted in the coming weeks by demand from banks and dealers tidying their balance sheet through quarter-end, according to analysts at JPMorgan.

"With volatility elevated and quarter end approaching, we expect balance sheet pressures at banks and broker dealers to increase over the next few weeks," analysts at the bank said in a report.

"This should help the most liquid sectors of the Treasury market outperform less liquid sectors," they said.

Copyright Reuters, 2011