The regional bloc ECOWAS had already suspended Guinea after special forces led by Lieutenant Colonel Mamady Doumbouya seized power on Sunday and arrested president Alpha Conde.
On Friday, the AU followed suit, tweeting that it had decided “to suspend the Republic of Guinea from all AU activities and decision-making bodies.”
Mediators from the 15-nation Economic Community of West African States (ECOWAS) also landed in the capital Conakry on Friday, AFP journalists saw.
ECOWAS Commission President Jean-Claude Kassi Brou is part of the delegation, as are the Nigerian, Ghanaian, Burkinabe and Togolese foreign ministers.
Increasing pressure on Guinea comes amid rising fears of democratic backsliding across West Africa, where strongmen are an increasingly familiar sight.
Guinea’s putsch has drawn parallels with its neighbour Mali, which has suffered two coups since August last year led by Colonel Assimi Goita, who was also a special forces commander
On Wednesday, ECOWAS called for Conde’s “immediate and unconditional release.”
It also urged “the immediate return to constitutional order” and demanded that the security forces “maintain a constitutional posture.”
Guinea’s putschists have formed a junta named the CNRD, which has dissolved the government and the constitution.
Doumbouya, hours after the coup, appeared on television and accused the Conde government of “endemic corruption” and of “trampling on citizens’ rights”.
He has pledged to open talks on forming a new government, but it is not yet clear when, or under what form, these may take place.
When faced with a similar predicament in Mali last year, ECOWAS imposed economic sanctions on the country, but lifted them after Mali’s ruling military committed to restoring civilian rule.
Public discontent in Guinea had been brewing for months over a flatlining Covid-hit economy and the leadership of Conde, who became the first democratically elected president in 2010 and was re-elected in 2015.
But last year, Conde pushed through a new constitution that allowed him to run for a third term in October 2020.
The move sparked mass demonstrations in which dozens of protesters were killed. Conde won the election but the political opposition maintained that the poll was a sham.
After the coup, the junta freed about 80 political activists detained under Conde and banned ex-ministers from leaving the country.
On Thursday, it also said it had temporarily frozen ex-ministers’ bank accounts.
Coup leader Doumbouya has nonetheless promised there will be no “witch hunt” against members of the former regime.
The military has also guaranteed the safety of Conde, whose whereabouts are unknown.
The coup was greeted with jubilation in some parts of Conakry, where residents in some districts came flooded the streets to applaud the soldiers.
But Conde supporters are bitter. Victor Leno, a schoolteacher and a member of Conde’s RPG party, said that “in one day, the military really came and buried this beautiful democracy”.
An RPG spokesman Mahmoudou Traore warned against trusting the military’s promises of a transition.
“They will stay in power for five, six (or) seven years,” he predicted.