(Adds context, seasonally adjusted rate, expansion of mining activity)
LIMA, Oct 15 (Reuters) - Peru's economy grew by a weaker-than-expected 2.57 percent in August from the same month a year earlier on rising copper production, state statistics agency Inei said Thursday.
The official reading marked a slight slowdown from June and July, when growth came in above 3 percent both months.
The economy contracted at a seasonally adjusted pace of 0.2 percent in August from July, Inei said.
A Reuters poll had forecast a 3.0 percent year-on-year expansion for August and the central bank had said it expected a pace similar to July's 3.26 percent rate.
The economy expanded 2.18 percent in the past 12 months through August and 2.55 percent in the first eight months of the year, from their year-earlier periods, Inei said.
A 13.30 percent surge in mining activity, driven by a strong surge in copper production, helped offset shrinking manufacturing, construction and fishing activity.
The central bank has said it expects copper output to continue to rise as new mines ramp up production. (Reporting By Teresa Cespedes; Editing by Chizu Nomiyama)