Reports say at least 58 people have been killed after troops in Guinea opened fire on an opposition rally.
A BBC correspondent says troops fired into protesters as they gathered in a stadium in the capital, Conakry.
About 50,000 people took part in the rally against Capt Moussa Dadis Camara, who seized power in the West African nation in a bloodless coup last year. 
It was triggered by indications he is to reverse a pledge not to run in a presidential vote planned for January.
Reports say at least two opposition leaders have been arrested.
Doctors said at least 58 bodies had been brought to hospital, many with bullet wounds.
France has issued a statement strongly condemning the "violent repression" of opposition demonstrators.
The BBC's Alhassan Sillah says the demonstrators have now been dispersed, but the military is out in force mounting checkpoints on many roads.
He says some opposition leaders appear to have been arrested and journalists have been targeted by the security forces.
Eccentric displays
Capt Camara staged a coup hours after the death of President Lansana Conte, who had ruled for more than two decades.
The military takeover initially had some popular support, but in recent weeks there have been several anti-government protests.
They appear to have been sparked by hints from Capt Camara that he may stand for president in January.
In Conakry, demonstrators gathered outside the capital's largest stadium, carrying placards reading "No to Dadis" and "Down with the army in power", according to the AFP news agency.
But the demonstration had already been banned and the stadium was closed and guarded by large numbers of police.
Clashes between police and demonstrators followed, with officers charging the crowds and firing live ammunition.
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.
Capt Camara's rule has been characterised by eccentric displays of power - such as forcing members of the elite presidential guard to beg for forgiveness on national TV after they roughed up a veteran officer.
Former aides and officials have been accused of corruption and links to the drugs trade, including the son of former President Lansana Conte, who was shown confessing on TV to smuggling cocaine.
