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"."Over the past year, protests in Guinea have been marked by appalling violence from all sides, including excessive use of force by the security forces," said Francois Patuel, West Africa researcher with the human rights group.And he warned "the deployment of a military unit notorious for human rights violations risks further inflaming the situation."Amnesty International "has verified videos and images showing members of the 'Berets Rouges', an elite military unit linked to previous human rights violations including unlawful killings and sexual violence, carrying rifles alongside police at a 15 October demonstration," the organisation said.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.On Monday a "dead city" strike gripped Conakry 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."With Guinea's opposition planning more demonstrations in the coming days, the authorities should take all necessary measures to ensure the situation does not spiral out of control. They must send a clear message to all security forces that unnecessary and excessive use of force will not be tolerated," Amnesty said.The rights group also called for "a thorough, impartial and effective investigation" into allegations that opposition head and former prime minister Cellou Dalein Diallo has been targeted for criticising the government.Last week Diallo said a man was shot dead and police had fired at his own car during a banned rally over the disputed elections.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.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.