The toll covers the period October 8-13, the days surrounding the October 11 vote which, according to the country's Independent National Electoral Commission (CENI), handed victory and another five-year term to incumbent Alpha Conde.
His main rival, opposition leader and former premier Cellou Dalein Diallo, has refused to recognise the outcome and urged supporters to take to the streets against what he labelled an "illegal" election tainted by mismanagement and fraud.
Amnesty listed six people killed in election-related violence in Guinea's capital city Conakry, including two victims shot in the back, and seven other fatalities in "violence between supporters" elsewhere in the country.
"There is clear evidence that members of Guinea's security forces were responsible for the death and injury of unarmed civilians," said Francois Patuel, Amnesty International's West Africa researcher.
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"There could be no justification for firing at these unarmed people, and no excuse for failing to hold those suspected of criminal responsibility to account," he added.
All seven defeated presidential hopefuls have dismissed the election as a charade and refused to recognise the official results, which gave Alpha Conde 57.85 percent of the vote, averting the need for a second round run-off.
Amnesty stressed that not all the violence came from the authorities but added that "as long as the use of firearms by the security forces against the population continues to be tolerated by the authorities, it will be impossible to build trust or put an end to Guinea's history of electoral violence."
The findings were backed up by witness statements.