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.
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NEW: Amnesty International says nine were killed on Thursday
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NEW: The people were killed in two locations
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Ban Ki-moon has warned "the situation is taking a worrying turn"
The @placeholder nation has been in a political stalemate over the disputed election, in which both men claim victory.