The African Union says the Zimbabwean military's takeover of power and detention of President Robert Mugabe "seems like a coup".
Its head, Alpha Conde, said the African Union demands an immediate return to constitutional order.
The military denies staging a coup, saying that Mugabe is safe and that it was acting against "criminals" surrounding him.
Their move follows a power struggle over who might replace Mugabe.
His vice‑president, Emmerson Mnangagwa was fired last week, making Mugabe's wife Grace the president's likely successor ‑ but leaving top military officials feeling sidelined.
93-year-old Mugabe has dominated the country's political scene since it gained independence from the UK in 1980.
Responding to the developments, Conde, who is also Guinea's president, said Zimbabwean soldiers "had obviously attempted to take power" and African Union had "serious concern" at the situation and "reiterates its full support to the country's legal institutions".
After days of tension and rumour, soldiers seized the state broadcaster ZBC late on Monday.
A Zimbabwean army officer, Major General Sibusiso Moyo, went on air to say the military was targeting "criminals" around President Mugabe.
He also insisted that it was not a military takeover.
Source: BBC
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