Human rights groups say 157 people were killed in September's crackdown
West African states have imposed an arms embargo on Guinea over the mass shooting of opposition supporters.
It comes amid growing criticism of the junta, led by Captain Moussa Dadis Camara, which seized power in December.
The Economic Community of West African States (Ecowas) condemned "atrocities" in September in which Guinean troops opened fire on an opposition rally at a stadium in the capital Conakry.
Human rights groups say 157 people died but the junta puts the toll at 57.
It says most of the victims were trampled to death rather than shot, as opposition activists say.
Human rights groups say soldiers raped and sexually abused women during the crackdown, and the International Criminal Court (ICC) has opened an investigation into the deaths.
The EU has called for Capt Camara to be tried for crimes against humanity, while the African Union has called for him to step down.
An Ecowas statement issued on Saturday at the end of a special summit in Nigeria said: "In view of the atrocities that have been committed... the authority decides to impose an arms embargo on Guinea".
The 15-member group called on its chairman, Nigerian President Umaru Yar'adua, to take "all necessary measures" to obtain the support of the African Union, European Union and United Nations to enforce the embargo.
Former colonial power France has already said it will stop weapon sales to the military government.
France on Friday urged its nationals - thought to number some 2,500 - to leave the mineral-rich country.
The French foreign ministry said the security situation in Guinea had worsened since the 28 September protests.
"Banditry, in particular armed robberies, have increased and there is no short-term prospect that the situation will improve," said a statement on the ministry's website.
Criminals had been following travellers from the airport and then robbing them when they get home, it added.
Meanwhile, Guinea's information minister, Justin Morel Junior, became the third minister to step down in a week, saying he no longer had the "moral strength" to speak for the government.
After September's protest, Capt Camara pointed the finger of blame at "controllable soldiers", adding that the opposition should not have held a banned rally.
When he took over the country last year, Capt Camara promised he would not stand in an election he scheduled for next January.
But recently he has hinted he would stand, sparking widespread condemnation and opposition protests.
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