The AU Peace and Security Council announced the suspension to press for "the restoration of constitutional order," the organization said in a statement issued at its headquarters in Addis Ababa.
"Council decides to suspend Mauritania's participation in all AU activities until the restoration of constitutional order in the country," said the statement.
The 53-nation group reiterated its firm condemnation of the Aug. 3 coup d'etat, in which military officers led by national police chief Ely Ould Mohamed Vall ousted President Maaouyia Ould Taya, who was in Saudi Arabia attending the funeral of King Fahd.
Taya on Wednesday landed in Niger's capital hours after learning about the coup.
The AU said it would send a ministerial delegation to Mauritania "to reiterate positions to the perpetrators of the coup d'etat and to engage them on the modalities for a speedy restoration of constitutional order."
The US and French ambassadors to Mauritania on Thursday met with Vall, who heads a 17-member Military Council for Justice and Democracy formed after the coup.
France is Mauritania's former colonial power, while the United States helps training Mauritania's troops to fight militants thought to be operating in the Sahara desert.
A US State Department official said Ambassador Joseph LeBaron demanded that Taya be restored to power after being summoned to the Foreign Ministry, where the coup leaders told him how they planned to strengthen democracy in the country.
The coup leaders have said that they will rule for two years to end the "totalitarian" regime of Taya, who himself took power in a 1984 coup. They have also pledged to respect all treaties and accords binding Mauritania.
"It was a sceptical audience they were talking to," commented the state department official, who declined to be named.
Both US and French ambassadors reiterated the condemnation of the coup. France says it will follow the situation closely.
In a mixture of moves to strengthen power and reconcile the nation of approximately 3 million, the coup leaders announced the dissolution of the National Assembly (parliament) on Thursday, while promising to maintain the constitution "supplemented by a Military Council charter."
It also pledged to maintain the government of Prime Minister Sghair Ould M'Bareck, who was appointed to the post by Taya in November 2003.
The Constitutional Council, the High Islamic Council, political parties and local governments would be kept in place, according to the Military Council.
Despite the worldwide outcry against the coup, Mauritania remains calm. Reports from the capital city of Nouakchott said Thursday people went to work as usual and traffic flowed freely.
Thousands of citizens even took to the streets in a show of support for the coup leaders.
Mauritania is one of the three Arab countries to have diplomatic ties with Israel. Taya, considered a pro-West president, was on the verge of being toppled in 2003. The coup-prone country said it foiled two other coup attempts in 2004.