Junta head Captain Moussa Dadis Camara denied knowledge of sexual assaults.
About 50,000 people were protesting over rumours that Capt Camara intends to run for president in an election schedule for next January, BBC News reports.
Opponents believe Camara is preparing to run as a candidate in a presidential election due to have taken place this year but now postponed to January. While he himself has made no formal declaration, his supporters have in recent weeks said there should be no impediment to him standing. Two days after Camara held a rally for his supporters in the city of Labe, a coalition of rival parties sought on Monday to hold their own event at a stadium in the capital Conakry. It was banned but thousands of people took to the streets and broke into the stadium anyway -- prompting an immediate and massive crackdown by security forces, Reuters reports.
Meanwhile, Guinea expert Gilles Yabi told the BBC's Focus on Africa programme that the rally was not a surprise.
"This is only the beginning of demonstrations and counter-demonstrations we can expect in the next few months," he said.
Should Capt Camara stand for president, he said, it would be a violation of the tacit agreement between military and civil forces which has kept him in power.
And it would mark a perpetuation of the kind of rule that Guinea has seen for the past decade - which the military had promised to sweep away, BBC News reports.