WASHINGTON - U.S. home prices fell by a seasonally adjusted 0.3 percent in August, bringing the 12-month decline to 3.6 percent, the Federal Housing Finance Agency said on Thursday.

The U.S. index is down 10.7 percent from its April 2007 peak.

The regulator's monthly index is calculated using purchase prices of houses financed with mortgages that have been sold to or guaranteed by mortgage finance companies Fannie Mae (FNM.N) or Freddie Mac (FRE.N).

(Reporting by Emily Kaiser; Editing by Theodore d'Afflisio)