Guinean police blocked several hundred women from marching through the streets of the capital Conakry in an opposition protest to demand "justice" for those killed during a series of bloody crackdowns on demonstrations.The women carried placards alleging brutality by security forces, in the latest eruption of discontent in Conakry, which was brought to a standstill on Monday by a "dead city" strike called by the opposition.Assembled near a mosque in the city suburbs, scores of women chanted "justice for our dead, death to the assassins" as they prepared to march into the city to protest in front of the Ministry of Security. But the group was prevented from marching by unarmed female gendarmes, who created a roadblock to hinder their passage."We want to go to shout our anger in front of the minister... who protects the killers," said Maimouna Diallo, of the main opposition UFDG party, told reporters. The opposition estimates that 98 protesters have been killed by police gunfire at peaceful demonstrations since President Alpha Conde came to power in December 2010.Amnesty International voiced concern on Wednesday at the number of protesters killed in Guinea - three in the last fortnight and 18 this year - urging the government to "take all necessary measures to ensure the situation does not spiral out of control".The political opposition in Guinea has been protesting against what it considers a violation by the authorities of an agreement reached in August over the appointment of local government officials elected in a hotly disputed vote on February 4.Monday's strike was over another issue that has plagued the West African country: the failure to resolve a pay dispute with teachers who began a walkout on October 3.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.