KHARTOUM (Reuters) - Sudan's annual inflation rate fell slightly to 46.4 percent in August, reflecting a 0.9 percent decrease in prices of consumer goods on the month, the Central Statistics Office said on Sunday. But in the year to August, inflation was reported at 38.1 percent, higher than in the same period last year when it was 35.5 percent. Prices have surged in Sudan since South Sudan seceded in 2011, taking with it three-quarters of the country's oil output. Oil is Sudan's main source of foreign currency, which it needs to support its pound and pay for food and other imports. The soaring cost of living is a major issue in the run-up to elections next year and has caused social unrest. Austerity measures and government plans to cut fuel subsidies prompted protests last year in which dozens were killed and hundreds injured. More demonstrations are expected in the coming month to coincide with the anniversary of those protests. President Omar Hassan al-Bashir has remained in power for 25 years despite armed rebellions, U.S. trade sanctions, an economic crisis, an attempted coup and an indictment from the International Criminal Court on charges of masterminding war crimes in the troubled western region of Darfur.