LUSAKA (Reuters) - Zambia's annual consumer inflation quickened to 6.6 percent in September from 6.3 percent in August, the Central Statistical Office said on Thursday. On a month-on-month basis, inflation rose by 0.3 percent after rising 0.1 percent in the prior month, the agency said. "The increase in the annual inflation rate was mainly attributed to price increases in electricity tariffs," the statistics agency said in a statement. (Reporting by Chris Mfula; Editing by Ed Stoddard)