Abidjan , Ivory Coast ( CNN ) -- At least nine unarmed protesters in Ivory Coast 's largest city were shot and killed by security forces Thursday , eyewitnesses told Amnesty International . The violence erupted as troops loyal to the incumbent president and supporters of his challenger confronted each other on the tense and chaotic streets of Abidjan . `` Amnesty International is appalled by this completely unjustified and disproportionate use of force and calls on the Ivorian security forces to stop these killings immediately , '' said Salvatore Sagues , the West Africa researcher for Amnesty , a human rights group . `` Those who opened fire on these people , as well as those who gave the order , will have to account for their acts , '' he said . The demonstrators -- part of mass street protests called by the presidential challenger , Alassane Ouattara -- had been marching from various locations in Abidjan `` in an attempt to seize the state-run RTI '' broadcasting offices when security forces fired on them , Amnesty said . Witnesses told CNN that exchanges of fire also raged outside a hotel that is serving as the headquarters of Ouattara , a former economist and prime minister who ran for president against incumbent President Laurent Gbagbo in a November 28 runoff . The West African nation has been in a political stalemate over the disputed election , in which both men claim victory . The country 's Independent Electoral Commission said Ouattara won the runoff , but the country 's Constitutional Council invalidated those results and declared Gbagbo the winner . Ever since , tension has filled the air in Abidjan . On Tuesday , Amnesty International said , `` Ouattara called for mass street protests to seize state radio and government buildings , still held by officials loyal to Laurent Gbagbo , who is refusing to leave office . '' Eyewitnesses told Amnesty International at least six people were shot dead by security forces in the neighborhood of Abobo . `` When we saw security forces near the police station of the 21st arrondissement , we raised our hands and told them that we were unarmed . They refused to answer and threw tear gas grenades . Then immediately they shot at us . I saw dead bodies in the street . I know three of them , '' one eyewitness told Amnesty International . Security forces near the Makassi crossroads shot tear gas and then fired on another group of protesters , killing three people , the human rights organization said . `` A young man , a car washer , who was not participating in the demonstration , was shot dead by two men wearing military uniforms , with hoods . The young man was standing in front of the garage waiting for drivers in order to wash their vehicles when two military ( personnel ) arrive . One of them tripped him up , he fell down . One of the military who was wearing sunglasses shot at him at point blank with a gun , '' an eyewitness told Amnesty International . CNN witnesses saw at least two dead bodies . One of the bodies was seen in front of U.N. headquarters , where there was a tent for the wounded . Another was seen in a slum near the Hotel Golf . Witnesses said he was a pro-Ouattara supporter who was shot by police because he was armed , but that account could not be confirmed . Heavy gunfire and mortars could be heard for at least an hour and up to three miles away from the hotel , where people protecting the Ouattara headquarters exchanged fire with forces loyal to Gbagbo . Soldiers loyal to Gbagbo were in combat posture , hiding in the bush around the hotel . Ex-rebel forces were trying to free blockades held by the pro-Gbagbo forces on the sole access road to the hotel . Witnesses spoke of confrontation at the RTI building , which has been surrounded by armored vehicles and troops loyal to Gbagbo since the crisis began . Also , police forces fired shots to disperse demonstrators in a pro-Ouattara neighborhood , witnesses said . The United Nations , African Union , European Union and other international bodies and leaders have called on Gbagbo to step down , but he has declined to do so . Read about the deadline set for Gbagbo to leave Ivory Coast . On Wednesday , U.N. Secretary-General Ban Ki-moon warned that the stalemate could lead to renewed fighting in a country that was wracked by civil war for several years . `` The situation is taking a worrying turn with unfolding events that could lead to widespread violence , '' Ban said in a written statement . The developments include recent threats by some commanders of the national security forces to resort to military options and also clashes on Monday between them and ex-rebels supporting Ouattara , the internationally recognized winner of the election . The International Criminal Court 's chief prosecutor , Luis Moreno Ocampo , told French media that he would prosecute people responsible for any deadly post-election violence . Sagues also warned that Ivory Coast is close to another civil war . `` Every effort must be made to prevent an escalation of violence . There is a very real threat that many more lives will be lost if the security forces continue to shoot at protesters indiscriminately , '' Sagues said . Journalist Eric Agnero contributed to this report .
NEW : Amnesty International says nine were killed on Thursday . NEW : The people were killed in different locations . Ban Ki - moon has said ` ` the situation is taking a worrying turn ''