* Sept inflation rises from 4.8 pct y/y in Aug
* Consumer prices up 0.9 pct m/m in Sept, 0.5 pct in Aug
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* For exclusive with Saudi c.bank gov: (Adds quotes, details, background)
By Asma Alsharif and Martina Fuchs
JEDDAH, Saudi Arabia/DUBAI, Oct 16 Saudi Arabia's annual inflation rose to an eight-month high of 5.3 percent in September, boosted by price rises of miscellaneous products and services, while monthly price growth almost doubled, data showed on Sunday .
Inflation in the biggest Arab economy and world's top oil exporter had hovered below 5 percent for most of 2011. It was 4.8 percent on an annual basis and 0.5 percent month-on-month in August.
Last month's annual consumer price growth of 5.3 percent was the highest since January, while month-on-month inflation was 0.9 percent, Central Department of Statistics data showed.
"External pressures might have had some effect but this is mostly about domestic demand," said Simon Williams, chief economist for the Middle East and North Africa at HSBC.
"Public spending is rising faster than elsewhere and credit growth is recovering more strongly. We continue to look for an end-year reading of around 6 percent."
Analysts had expected consumer prices to gain momentum this year after the government pledged early in 2011 to spend an estimated $130 billion, or nearly 30 percent of annual economic output, on housing, job creation and other measures to improve social welfare over an unspecified period.
"Always in the second half of the year, which includes summer vacations, Ramadan, religious holidays and restarting of the schools, these factors result in increased spending and prices," said Abdulhamid Al-Amri, member of the Saudi Economic Association think tank.
"I expect that from now until the end of the year the prices will continue rising."
A Reuters poll of analysts in September forecast average inflation of 5.1 percent in 2011, slightly down from 5.3 percent in 2010.
Food costs, which account for 26 percent of Saudi consumer expenses, increased 0.4 percent month-on-month in September after a 1.5 percent jump in August, the data showed.
Housing and utility prices, making up 18 percent of the consumer basket, rose 0.6 percent after a 0.7 percent climb in August. The products and services component saw a 3.9 percent spike in September.
The International Monetary Fund said in August that the kingdom, which pegs its riyal currency to the U.S. dollar, needed to keep a close eye on inflationary pressure following the planned increase in social spending.
But in a Reuters interview on Saturday, central bank Governor Muhammad al-Jasser said interest rate settings were appropriate at the moment with no signs of inflation coming from monetary stimulus.
Jasser said earlier this month that he was "not worried" about inflation levels and expected them to continue to decline.
Saudi Arabia's economy is forecast to expand 6.2 percent in 2011 following 4.2 percent growth in 2010, helped by robust crude oil prices and generous government spending, according to the analysts polled by Reuters last month. Growth is expected to slow to 4.5 percent next year, partly because of a weakening of the global economy. (Reporting by Asma Alsharif and Martina Fuchs; Editing by Andrew Torchia)