Guinea opposition leader Sidya Toure has been charged with plotting to stage a coup, his lawyer has said.
Mr Toure was prime minister from 1996 to 1999
The former prime minister was detained on Monday and freed on bail after being charged, the lawyer said.
Senior army official Colonel Mamadou Camara was also reportedly charged.
President Lansana Conte, 69, who seized power in a coup in 1984, was re-elected with more than 90% of the vote in December's polls, which were boycotted by the opposition.
Mr Toure and Col Camara had to surrender their passports before being freed, said defence lawyer Christian Sow.
Last week, Security Minister Moussa Sampil announced on national television that members of Mr Toure's Union of Republican Forces (UFR) party had discussed killing Mr Conte and dissolving the country's government at a meeting on 10 March.
Mr Toure told the Associated Press news agency that he was not at the meeting and he denied any knowledge of the alleged assassination plot.
Conte won an overwhelming victory in the December vote
Senior officials of Mr Toure's party were arrested earlier this month for allegedly plotting a coup.
The International Federation of Human Rights Leagues (FIDH) has branded the government in Guinea as a sham democracy, denouncing widespread rights
abuses in the country.
The human rights group criticised the systematic repression of opposition parties, barriers to freedom of expression, a culture of impunity and discrimination against women.