Yields on agency mortgage-backed securities that guide home-loan rates rose for a fifth day to the highest level since August 2011, extending a surge sparked by a potential slowing of the Federal Reserve’s debt buying.

Bonds have tumbled worldwide after Fed Chairman Ben Bernanke said the next day at a news conference that the central bank may ‘moderate’ the pace of its $85 billion of monthly debt buying later this year and end the purchases around the middle of 2014.