ACCRA (Reuters) - Ghana's economic growth slowed to 2.5 percent in the second quarter, compared with a year earlier, as oil production fell, provisional official data showed on Wednesday. Ghana saw sustained GDP growth above 8 percent until 2013 on its exports of gold, cocoa and oil. It has since seen a slump in part because of lower global commodity prices and also due to a fiscal crisis that forced the country to secure an aid deal with the International Monetary Fund, which began last year. "The economy is growing but not at the same rate as the first quarter, when it was 4.8 percent," said government statistician Philomena Nyarko. The slowdown in the second quarter was mainly due to a halt in oil production caused by a technical fault at the country's main production vessel, Nyarko said In the second quarter of last year, the economy grew by a revised 3.8 percent from a year earlier, the statistics office said. The health of the economy is a major issue for voters in the run up to an election in December, when President John Mahama faces opposition leader Nana Akufo-Addo in what is expected to be a tight vote. The government says it has fixed fiscal problems and the economy will return to a growth rate above 8 percent in 2017. The opposition says only it can rebuild the economy and put it on a sustainable footing. Ghana's producer price inflation (PPI) rose to 11.1 percent year-on-year in August from a revised 10.4 percent in July, the statistics office said on Wednesday. PPI is a major component of consumer inflation, which has for years remained above government targets. (Reporting by Kwasi Kpodo; Writing by Matthew Mpoke Bigg; Editing by Susan Fenton)