(Adds remarks and context on inflation and potential growth rate)
By Mitra Taj and Teresa Cespedes
LIMA, Jan 15 (Reuters) - Peru's central bank surprised the market by cutting the benchmark interest rate 25 basis points to 3.25 percent after the global minerals exporter posted its worst monthly economic expansion since 2009.
The central bank said the move did not mean the start of a series of rate reductions.
All but one of 20 analysts polled by Reuters earlier this week said they thought the monetary authority would hold the interest rate steady for a fourth straight month to avoid stoking a steeper slide in the local sol currency .
A lower interest rate could prompt a broader sell-off of soles.
But concerns about the ongoing economic lull appear to have weighed more heavily at the central bank.
"Most recent indicators of productive activity continue showing a weak economic cycle, with GDP growth rates under potential throughout 2014 and significant drops in primary activities because of negative supply factors," the central bank said in a statement.
Earlier on Thursday, the state statistics agency released data showing the economy grew by just 0.31 percent year-on-year in November - the weakest pace since July 2009 and far from the 1.55 percent expansion forecast in a Reuters poll.
The central bank did not mention volatility in currency markets as it did in its statement last month, when it held off on lowering the interest rate because of the sol's slide.
Late last month, the central bank tightened rules on currency derivatives to curb speculation it says helped fuel the sol's 6.4 percent weakening against the U.S. dollar in 2014.
After growth data for November was posted, the sol slid past the psychological barrier of 3 per dollar for the first time in more than five years.
The central bank said it now expects inflation to converge "more quickly" to its goal of 2 percent this year, and added that declining global oil prices are starting to spill over into the local economy.
In Peru, oil prices are expected to ease inflationary pressure.
The annual inflation rate rose slightly in December to 3.22 percent - above the bank's 3 percent target ceiling for the third month in a row.
The economy grew 2.5 percent in the first 11 months of 2014.
The central bank views the potential growth rate, the pace the economy can grow without too much inflation, at 5.3 percent. It lowered the interest rate twice last year and once in 2013 as the economy started to slow.
Reporting by Mitra Taj and Teresa Cespedes; Editing by Lisa Shumaker and Diane Craft