Thousands of people meanwhile took to the streets to celebrate a coup on Thursday’s and express support for the soldiers, witnesses said.
“As of today, Niger will not be represented in our activities,” said Mull Sebujja Katende, who presides over the African Union’s peace and security council.
“We have condemned the coup and imposed sanctions on Niger: Niger is suspended from all activities of the AU,” he said.
The body also called for Niger to revert to the constitution in place before an August referendum which allowed Tandja to stay in office, potentially for life.
International condemnation of the coup grew with the US calling for a “speedy return to democracy” and former colonial ruler France demanding fresh elections “in the coming months”.
Niger’s military junta meanwhile authorised free movement in and out of the country after capturing the president and sacking his government.
“The situation is under control,” junta spokesperson Colonel Goukoye Abdoulkarim told journalists.
In the capital Niamey, thousands of people gathered outside the military barracks to express support for the junta, shouting “Long live the soldiers” and “We are in your support,” an AFP correspondent said.
A prominent junta member, Colonel Djibrilla Hamidou Hima, addressed the crowd and told people to spread the word that country was “doing fine”.
Hundreds of people also gathered in the western city of Dosso “to express their support for the junta”, trader Mahamadou Boureima said by telephone.
People on motorcycles, in cars and on foot shouted “long live the council (junta)” and “Down with the regime of Tandja”, the trader said.
There were also celebrations in Tahoua, the home region of leading opposition figure Mahamadou Issoufou, said residents.
An opposition coalition, the Co-ordination of Democratic Forces for the Republic, meanwhile called on its members to “participate massively” in a pro-junta rally in Niamey on Saturday.
The army on Thursday stormed the palace during a cabinet meeting and seized Tandja and detained his ministers before announcing it was suspending a constitution that the 71-year-old forced through with the contested August referendum.
The junta swung into action late on Thursday with a call for support from the 15 million population, promising to make the world’s third largest uranium producer a beacon of “good democracy and governance” after months of political turmoil.
Calling itself the Supreme Council for the Restoration of Democracy (CSRD), it dissolved the government of the poverty-stricken nation, then held its first meeting with senior officials of ministries on Friday.
In his first public speech to reporters, junta leader Major Salou Djibo said he would set up a consultative working council to take collective decisions.
Tanks and trucks mounted with machine guns were stationed around the presidential palace, the prime minister’s office and the foreign ministry. The junta confirmed it was holding Tandja at a military establishment in the capital and said he was well.
At least three soldiers were killed during fierce gun battles that accompanied the coup. A watch tower at the palace in downtown Niamey was hit by a rocket while a gate was also damaged.
EU foreign affairs chief Catherine Ashton on Friday condemned the coup, as did France, while AU chief Jean Ping said there should be “zero tolerance” for taking power by force.
Niger has been embroiled in political crisis for nearly a year since Tandja, who was in power for more than a decade, launched his bid to extend his rule.
Talks between Niger’s government and the opposition to end the political stand-off were suspended last week, having repeatedly stalled since they began on December 21. AFP