The body's Peace and Security Council voted to suspend Togo on Friday and urged the 53-member AU "to take all measures to restore constitutional order to Togo as soon as possible", Council Commissioner Said Djinnit said.
The transfer of power to Faure Gnassingbe by Togo's army on 5 February has been roundly condemned by African leaders.
The 15-member council, modelled on the UN Security Council, was meeting at ambassadorial level amid growing calls for Gnassingbe to vacate the leadership office.
Togo, which is a member of the body but was suspended after Gnassingbe took power, was not represented at the meeting and the Togolese ambassador to the African Union, Koffi Esaw.
He said he had been asked to leave the chamber.
'We are suspended'
"They asked me to leave the room because we are suspended but the president told me they might possibly need me during the debate," he said.
The African Union has urged Togo
to restore constitional order
AU commissioner Alpha Oumar Konare was the first to blast the military power play a "coup d'etat" and has recommended that the ECOWAS sanctions be extended to include the entire continent.
But with international pressure ratcheting up, diplomats said support for sanctions was waning.
"There is fear among some member states that if the AU imposes sanctions it will be more difficult for Faure Gnassingbe to reverse the situation and step down," one AU diplomat said on condition of anonymity.
Unsuccessful defusing attempt
The 39-year-old Gnassingbe has tried to defuse the mounting pressure by agreeing to call presidential elections within 60 days but insists on remaining in office until then, a stance that has done little to appease his critics.
In addition to the uproar in Africa, the European Union has threatened to slap unspecified "measures" on Togo, joining the United States in backing AU and ECOWAS efforts to restore constitutional rule and democracy.
On Thursday, Gnassingbe sought counsel from veteran African leaders in Gabon and Libya and suggested that he was considering whether to heed the calls to step down before contesting the election.
Gnassingbe pledged to take "important steps" to resolve the crisis beginning on Friday, Libya's JANA news agency reported.