Tensions rose in Harare on Tuesday as armoured vehicles, military police and soldiers from Zimbabwe's powerful military drove through the outskirts of the capital.
It comes a day after the head of the armed forces said he was prepared to "step in"to end a purge of supporters of sacked vice-president Emmerson Mnangagwa.
Witnesses in the city reported several lorries full of military personnel and at least six armoured vehicles on roads approaching the city in the late afternoon, though residents said there was no sign of troops in the centre of Harare, the airport, government broadcasters or the residence of president Robert Mugabe.
A second column of around a dozen vehicles was reported moving down the same road several hours later.
The deployments of military vehicles and soldiers led many to believe a coup was underway against Mr Mugabe, the only leader Zimbabwe has known in 37 years of independence.
It is still unclear who ordered the military movement, though it comes amid an unprecedented challenge to the 93-year-old president from the armed forces.
Zimbabwe was plunged into crisis when Mr Mugabe sacked Mr Mnangagwa , a 75-year-old veteran of Zimbabwe’s liberation wars, last week.
The former intelligence chief and long-time associate of the president had been viewed as his most likely successor, and is thought to have significant support within Zimbabwe’s security establishment.
Grace Mugabe
Mr Mnangagwa’s downfall opens the way for his arch rival, Mr Mugabe’s 52-year-old wife Grace, to take power when the ailing president dies, resigns or is ousted.
General Constantine Chiwenga, the head of Zimbabwe's military, warned on Monday that troops would intervene if long-term political allies continued to suffer.
“We must remind those behind the current treacherous shenanigans that, when it comes to matters of protecting our revolution, the military will not hesitate to step in.
"The current purging, which is clearly targeting members of the party with a liberation background, must stop forthwith," Mr Chiwenga said in a statement read to reporters at a news conference packed with senior officers.
Neither the president nor his wife has responded to the general’s remarks but a strong denunciation from the ruling party youth wing on Tuesday signalled that Grace Mugabe’s supporters were prepared to defend her.
“We will not fold out hands to allow a creature of the constitution to subvert the very constitution which establishes it,” said Kudzai Chipanga, who leads the Zanu-PF Youth League, said at the party’s headquarters in Harare.
“Defending the revolution and our leader and president is an ideal we live for and if need be it is a principle we are prepared to die for.”
The failure of the president to make any statement since the crisis broke suggests he "is not in full control", said Piers Pigou, an expert on Zimbabwe with the International Crisis Group, who is based in neighbouring South Africa.
“It is very unclear how this will play out and there is a certain amount of wishful thinking from those who would like to see Mugabe arrested or dragged off ... but his silence suggests an executive which is not in charge of the situation,” he added.
Mr Mugabe was chairing a weekly cabinet meeting in the capital on Tuesday, which continued through the afternoon.
His rule has been anchored by support from the military but the ageing leader does not tolerate public challenges.
As Mr Mugabe has systematically dismissed veterans of the liberation struggle from party posts, the top echelons of Zanu-PF are now stacked with officials who did not fight in the independence war.
War veterans broke ranks with him in 2016 and have vowed to form a broad front with the opposition to challenge his long rule.
‘Coup ... by marriage certificate’
Chris Mutsvangwa, the head of the war veterans' group, told reporters in Johannesburg last week that Grace Mugabe was "a mad woman" who had won power through a "coup ... by marriage certificate".
The first lady is a deeply divisive figure in Zimbabwe with limited popular support. Her image has been tarnished after an alleged assault on a model she had found in the company of her sons in a luxury apartment in Johannesburg in September.
Granted diplomatic immunity after the incident, she was allowed to leave South Africa despite a police inquiry and denies any wrongdoing
Reports of extravagant purchases, including property in South Africa and a Rolls-Royce, have also angered many Zimbabweans.
Pictures of one of the first lady’s sons apparently pouring most of a bottle of champagne over a luxury watch worth tens of thousands of dollars in a nightclub were shared widely on social media this week.
The former junior administrator is detested by many of the independence-era war veterans, who once enjoyed a privileged role in the ruling party under Mugabe, but who have increasingly been banished from senior government and party roles in recent years.
The crisis comes at a time when Zimbabwe faces severe economic problems. The country is struggling to pay for imports due to a shortage of dollars, which has also caused acute cash shortages.