Zimbabwe’s military has placed President Robert Mugabe under house arrest in the capital Harare, South African President Jacob Zuma says.
Mr Mugabe told Mr Zuma in a phone call that he was fine, the South African leader’s office said.
Troops are patrolling the capital, Harare, after they seized state TV and said they were targeting “criminals”.
The move may be a bid to replace Mr Mugabe with his sacked deputy, Emmerson Mnangagwa, BBC correspondents say.
Mr Mnangagwa’s dismissal last week left Mr Mugabe’s wife Grace as the president’s likely successor.
Mr Mugabe, 93, has dominated the country’s political scene since it gained independence from the UK in 1980.
After days of tension and rumour, soldiers seized the state broadcaster ZBC late on Tuesday.
A Zimbabwean army officer, Major General Sibusiso Moyo, went on air and denied there was a coup, but said the military was targeting “criminals” around President Mugabe.
Maj Gen Moyo also said Mr Mugabe and his family were “safe and sound and their security is guaranteed”. It is not clear who is leading the military action.
Since then military vehicles have been out on the streets of Harare, while gunfire has been heard from northern suburbs where Mr Mugabe and a number of government officials live.
In a statement, Mr Zuma’s office said: “President Zuma spoke to President Robert Mugabe earlier today who indicated that he was confined to his home but said that he was fine.”