PORT-AU-PRINCE, Haiti, Aug 9 (Reuters) - Haitians voted Sunday for the first time in four years in a test of stability for an impoverished country continually rocked by political turmoil. Men armed with rocks and bottles attacked polling stations in the capital of Port-au-Prince and about 50 of 1,500 voting centers around the country were "affected" by a mixture of violence and bureaucratic problems, according to Haiti's official Electoral Council. The council's head, Pierre-Louis Opont, did not elaborate and said it was too early to know how many ballots were impacted. Voting was extended two hours at some polling stations that opened late or were forced to suspend voting. The Caribbean nation of about 10 million people has struggled to build a stable democracy ever since the overthrow of the dictatorship of the Duvalier family, which led Haiti from 1957 to 1986, and ensuing military coups and election fraud. The country was also devastated by an earthquake in 2010 that flattened large parts of the capital, including the presidential palace, killings tens of thousands of people. Haiti's parliament dissolved in January after scheduled legislative elections in 2011 and 2014 were canceled.