Opposition parties and civic groups in Burkina Faso have called a mass rally for Sunday in protest at the army takeover after the resignation of President Blaise Compaore.
They said the management of the transition belonged to the people and should not be confiscated by the army.
It came hours after the army said Lt-Col Isaac Zida, second-in-command of the presidential guard, had been chosen as the nation's transitional leader.
Mr Compaore has fled to Ivory Coast.
"The victory born from this popular uprising belongs to the people, and the task of managing the transition falls by right to the people," opposition groups said in a statement.
"In no case can it be confiscated by the army."
There were protests earlier this week after Mr Compaore sought to amend the constitution and extend his long hold on the presidency.
On Thursday, protesters set fire to parliament and government buildings in the capital Ouagadougou.
The BBC's Thomas Fessy, following events from Senegal, says there is growing concern among the population that events may now be hijacked by a military coup.
But in a country where the ousted president has dominated the political scene for nearly three decades, the opposition remains weak and the turnout at the rally will be a measure of its credibility, our correspondent says.
The army's response will show if the new man in charge, Lieutenant Colonel Zida, is ready to respect the wishes of the people, our correspondent adds.
Under the country's constitution, the president of the Senate should take over after the national president resigns, with elections taking place between 60 and 90 days afterwards.
The African Union has called for a "civilian-led transition" culminating as soon as possible in "the holding of free, fair and transparent elections".
In a statement, AU chief Nkosazana Dlamini-Zuma urged the military to "refrain from any acts or statements that may lead to further instability".
The US state department urged an immediate transfer of power to civilian authorities in Burkina Faso and a move towards free and fair presidential elections.
The unveiling of Lt-Col Zida as interim leader came after what analysts say was a 24-hour power struggle within the army.
The army statement's was signed by army chief General Honore Traore, who had declared himself head of state in the immediate aftermath of President Compaore's resignation.