Yields on Fannie Mae and Freddie Mac mortgage securities rose to the highest level since the end of last year, after the conclusion Wednesday of the Federal Reserve's unprecedented purchase of the debt.

Yields on Fannie Mae's current-coupon 30-year fixed-rate mortgage bonds climbed 0.03 percentage point to 4.55% Thursday morning, the highest since Dec. 31, according to data compiled by Bloomberg News. The move tracked an advance in yields on benchmark government notes after a report showed initial jobless claims dropped.

The difference between yields on the Fannie Mae securities and 10-year Treasuries widened for a third day, rising about 0.01 percentage point to 0.69 percentage point.

On March 10 that spread fell to 0.59 percentage point, the lowest since at least 1984, as the Fed's purchases of $1.25 trillion of agency mortgage bonds approached their scheduled conclusion.

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