The African Union (AU) has given Burkina Faso’s military a two-week deadline to hand power to a civilian ruler or face sanctions.
The AU said the army had acted unconstitutionally when it took over after President Blaise Compaore was forced to resign on Friday.
The military said a civilian-led transitional government would be established as quickly as possible.
Mr Compaore quit after mass protests at his bid to extend his 27-year rule.
On Saturday, the military named Lt Col Isaac Zida, previously second in command of the presidential guard, as the new interim ruler.
A popular revolt led to Mr Compaore’s resignation, but the military takeover was against democracy, said AU official Simeon Oyono Esono, following a meeting of the body’s Peace and Security Council in Ethiopia.
The AU will apply sanctions against Burkina Faso if the military fails to give up power within two weeks, Mr Esonohe told Reuters.
The BBC’s Emmanuel Igunza in the Ethiopian capital Addis Ababa says the sanctions could include suspension of Burkina Faso’s AU membership and a travel ban on military officials.