Col Mamady Doumbouya has been sworn is as Guinea’s interim president after leading a coup that saw the overthrow of Alpha Condé.
The former French legionnaire, 41, becomes Africa’s second-youngest leader, after Mali’s Assimi Goïta, 38, who also staged a military takeover.
Col Doumbouya is barred from contesting future elections under plans to restore civilian rule announced this week.
The 5 September coup has been widely condemned.
Both West Africa body Ecowas and the African Union have suspended Guinea.
Ecowas also imposed sanctions against the coup leaders and demanded a return to constitutional order within six months.
Speaking at the Mohammed V palace in Conakry, the new president said his mission was to “refound the state” by writing a new constitution, tackling corruption, changing the electoral system and putting in place “free, credible and transparent” elections, according to the AFP news agency.