CONAKRY, Guinea (AP) — Pre-election violence in Guinea has killed at least three people and injured some 50, a hospital official said Saturday, as the United Nations West Africa head called for calm a day before Guineans are to vote for president.

President Alpha Conde is running against seven candidates, including main opposition leader, Cellou Dalein Diallo. Conde defeated Diallo in a 2010 election marked by clashes between their supporters along ethnic lines. The country has a history of electoral violence that experts worry will return with the Oct. 11 presidential election.

A hospital worker, who insisted on anonymity because he is not authorized to speak to the press, said the deaths and injuries have been caused by violence since Thursday.

Mamadou Lamarana Diallo said Saturday he saw an officer open fire on demonstrators, killing his friend, in a Conakry suburb known as an opposition stronghold.

Demonstrators on Friday clashed near the home of opposition candidate Diallo. Taxi driver Cherif Bah said his friend was fatally stabbed in his car.

At least 33 people were injured in the fighting Friday between Diallo's Union for the Democratic Forces of Guinea party and Conde's Rally of the Guinean People-Rainbow Party supporters, said Interior Minister Mahmoud Cisse.

The U.N. West Africa office head, Mohammed Ibn Chambas, called for calm on Saturday after meeting with international monitors.

The International Federation for Human Rights also called on candidates to appeal to their supporters for calm, as Guinea holds its second democratic elections in more than half a century. Guinea suffered under decades of corrupt dictatorship after independence from France in 1958.

This story has been corrected to show that the taxi driver's name is spelled Cherif.