About 50,000 people are said to have demonstrated against the junta
The International Criminal Court (ICC) has opened an investigation into the Guinean military's brutal suppression of an anti-government protest.
The Hague court says it is deciding whether the events of 28 September amount to crimes against humanity.
The prosecutors say there is evidence that women were "abused or otherwise brutalised" during the crackdown.
Rights groups say 157 people died after soldiers fired at protesters in a sports stadium in the capital Conakry.
Guinea's military rulers, who deny responsibility for the deaths, say about 57 people died - and most of them were trampled to death.
ICC Deputy Prosecutor Fatou Bensouda labelled the crackdown on protesters "appalling and unacceptable".
"From the information we have received, from the pictures I have seen, women were abused or otherwise brutalised on the pitch of Conakry's stadium, apparently by men in uniform," she said.
"It must never happen again. Those responsible must be held accountable."
The ICC announcement comes amid growing pressure on the Guinean government.
On Wednesday the EU's development chief called for junta leader Captain Moussa Dadis Camara to be tried for crimes against humanity.
Karel de Gucht said the crackdown on protesters was "an act of brutality never seen before".
And concern has also been raised over a mining deal which a Guinean minister said had been agreed this week, which could see a Chinese firm pumping $7bn (£4.5bn) into the country.
The US-based Human Rights Watch group said the deal "sends the wrong message at the wrong time".
"There's a real risk that these investments could entrench and embolden and enrich an already abusive government," the AP news agency quoted HRW's Arvind Ganesan as saying.
"After widespread abuses have taken place in Guinea, for the government to be able to tout a $7bn deal with the China International Fund says that they are above criticism."
China has not confirmed the deal, but foreign ministry spokesman Ma Zhaoxu defended continuing trade ties saying the countries shared a "traditional friendship".
"Our co-operation is based on equality and mutual benefit and is in line with international norms and with the fundamental interests of both peoples," he said, according to the AFP news agency.
The junta, which took power last December in a bloodless coup, also appears to be facing divisions in its own government with two civilian ministers resigning this week.
Radio France International reported that Minister of Labour Alpha Diallo handed in his resignation because he disagreed with the brutality of the army.
"The 28 September shook me as far as my religious and moral convictions are concerned," he told the station.
It followed the resignation of the minister of agriculture, who said he could no longer show solidarity with the government.
When Capt Camara took over the country, he promised he would not stand in an election he had scheduled for next January.
But recently he hinted he would stand, sparking widespread condemnation and opposition protests.