BRATISLAVA, Oct 27 (Reuters) - Slovak producer prices rose less than expected in September thanks to cheaper oil, data showed on Friday, but analysts still predicted the central bank would tighten its monetary policy further later this month. Producer prices fell by 0.7 percent on a monthly basis in September, putting the annual inflation rate at 7.5 percent, the Slovak Statistics Office said. Analysts polled by Reuters had forecast producer prices to have risen by 0.1 percent, month-on-month, for an annual rate of 8.4 percent. "The category of refinery products, which showed the biggest decline, provided the main contribution to the drop," said CSOB Bank analyst Silvia Cechovicova. Refinery goods were down 7.1 percent month-on-month, the biggest drop in the past 10 months, after a 0.3 percent rise in August. "It will take several months to confirm the downward direction. I do not see any major implications for the monetary policy from this figure, A key reading to watch is the CPI," said ING Bank's senior analyst Lucia Steklacova. Slovak factory-gate prices have shot up this year due to rising oil costs and subsequent hikes in natural gas prices, but producer prices have only a minor impact on consumer price inflation which is the central bank's main focus. The lower-than-expected PPI rate followed a slow-down in consumer inflation in September, but analysts said the central bank would probably raise its interest rates again by 25 basis points at the end of October to keep off inflation risks. The central bank has increased the key-two week repo rate by 175 basis points so far this year to 4.75 percent. It has warned more hikes may be needed because of risks stemming from an uncertain outlook for utility prices and fast economic growth. "The PPI number obviously is a surprise on the downside, but it's quite high and we do not think that this will change much for monetary policy," said Danske Bank analyst Lars Christensen. ((Reporting by Martin Santa ; bratislava.newsroom@reuters.com; Editing by Gerrard Raven; Reuters Messaging: martin.santa.reuters.com@reuters.net; +421 2 5341 8402)) Keywords: ECONOMY SLOVAKIA PPI