Six Guinean opposition figures remained in custody at an "unknown location" on Sunday after they were arrested ahead of planned protests against a possible bid by octogenarian President Alpha Conde to seek a third term, their lawyer said.
The six men spearheaded the formation in April of the National Front for the Defence of the Constitution (FNDC), grouping members of the West African country's main opposition parties, civil society associations and trade unions.
The group, which won the backing of the powerful teachers' union on Saturday, has called for a general strike and nationwide protests on Monday despite fears of violence.
"Since they were picked up Saturday at the home of their leader (Abdourahmane Sanoh), they were... questioned for four hours, then taken to an unknown location," lawyer Salifou Beavogui told AFP.
Police accuse them of "disturbing public order and remarks inciting revolt, which they have repeatedly rejected," Beavogui said.
Conde, 81, last month called on the public to prepare for a referendum and elections, stirring talk that he is planning to overcome a constitutional ban on a third term in office.
Himself a former opposition figure, Conde has cracked down on protests against an amendment that would allow him to extend his rule over the mineral-rich but poor former French colony.
The opposition says about 100 people have been killed since Conde became Guinea's first democratically elected president in 2010, winning re-election five years later.
The FNDC said the security forces who arrested the six men at Sanoh's home wore masks.
Another two activists were arrested elsewhere, the FNDC said.
The umbrella grouping reiterated its "call for an unprecedented mobilisation (against) those determined to promote a presidency for life".
The next presidential election is to be held late next year.