By Luciana Lopez NEW YORK, June 24 (Reuters) - Prices for U.S. Treasuries resumed their slide on Monday, with benchmark yields at a nearly two-year high as worries continued about an exit in coming months by the U.S. Federal Reserve from its massive bond-buying program. Fed Chairman Ben Bernanke sparked a selloff last week after he said the U.S. central bank could scale back its $85-billion-per-month purchases of Treasuries and mortgage-backed securities this year as the world's biggest economy gains traction. Bernanke's words took yields on benchmark U.S. 10-year notes to their highest since August 2011 - a rise that continued on Monday. "It doesn't matter that the Fed did not 'want' rates to rise," said Chris Bury, head of U.S. rates trading & sales at Jefferies in New York. "Once it starts it is hard to stop." U.S. 10 year-notes fell 19/32 in price on Monday to yield 2.614 percent from 2.542 percent late on Friday. The yield on Monday hit its highest since Aug. 2, 2011, several days before rating agency Standard & Poor's cut the U.S. sovereign rating from its prized AAA. The 30-year Treasury bond slumped 5/32 to yield 3.603 percent, from 3.595 percent on Friday. In a Reuters poll after last week's Fed meeting, primary dealers largely saw the Fed slowing its asset purchases in September or December, with a smattering of other answers through the first quarter of 2014. The potential Fed pullback has hit a range of assets around the world, including stocks and bonds in emerging markets and the U.S. stock market. The sinking Treasury prices could also be worrisome for the $99 billion slated for this week. The Treasury will sell $35 billion of 2-year notes on Tuesday, $35 billion of 5-year notes on Wednesday and $29 billion in 7-year notes on Thursday. Analysts said the selloff will cool at some point, but perhaps not quite yet. "I like to think of this in terms of being a brushfire," William O'Donnell, head Treasury strategist at RBS Securities in Stamford, Connecticut. "There still appears to be tinder out there to burn, in other words sellers that can't get out or need to get out," he said. "It's anyone's guess where this stops."