Robert Mugabe has asked for "a few more days, a few more months" as he faces calls to stand down.
It comes after he made his first public appearance since an apparent military coup, turning up at a graduation ceremony.
The deposed leader is chancellor of the University of Zimbabwe and goes to the event each year.
Wearing an academic gown and mortar board, he was cheered by the crowd as he opened the ceremony.
Sky News' David Bowden, who is in the capital Harare, said: "Mugabe is not known as a shrinking violet. He's supremely confident in his own abilities, whatever they might be. I suspect this might be a final act of defiance."
Mr Mugabe's public appearance comes amid reports he has been under house arrest since the coup began on Tuesday.
The Zimbabwe war veterans' association said the leader asked for "a few more days, a few more months".
But Botswana's President, Ian Khama, has said he should stand down.
He said: "I don't think anyone should be president for that amount of time. We are presidents, we are not monarchs. It's just common sense."
Branches of the ruling party have turned against him, issuing votes of no confidence. Mashonaland East province has passed the vote, with another 10 understood to be following.
Mr Mugabe reportedly refused to resign at a meeting with generals and was pictured for the first time last night.
In the images taken at State House in Harare, he appeared smiling with an army chief and South African envoys.
The 93-year-old reportedly arrived in his motorcade from his private residence for the crunch talks, which also included officials from the Southern African Development Community (SADC).
"They met today. He is refusing to step down. I think he is trying to buy time," said a source close to the army leadership who declined to be named.
Mr Mugabe has been in military custody, reportedly with his wife Grace, since the army stepped in earlier this week, as soldiers blockaded key roads and took over state television.
Bowden said: "He will know that the clock is ticking substantially faster than it has done over the past week.
"He will be out and about today presumably making sure people know he is still a man in command... so that when he does appear on television and says 'I've decided I'm going to gracefully move along' that he will maintain some kind of dignity."
Images of the meeting, published by The Herald newspaper, showed him dressed in a navy blazer and grey trousers alongside army boss General Constantino Chiwenga.
In one photo, he was pictured smiling and shaking hands with the military chief.
South Africa's President Jacob Zuma, speaking in parliament, said the political situation "very shortly will be becoming clear".
Grace Mugabe, who was reportedly being lined up as her husband's successor, was not in the photos.
There was also no sign of former vice president Emmerson Mnangagwa, whose firing last week angered supporters in the military as concern grew that Mrs Mugabe would take his place.
Morgan Tsvangirai, a former prime minister and long-time opponent of Mr Mugabe, said he must resign "in the interest of the people".
He added that "a transitional mechanism" would be needed to ensure stability.
Wilf Mbanga, the founder, publisher and editor of The Zimbabwean newspaper, told Sky News he believed there were sticking points to Mr Mugabe resigning - the president wants security for his family and to keep his wealth, and assurances he won't be prosecuted when he steps down.
Mr Mbanga also claimed foreign ministers from the Southern African Development Community want Mr Mugabe to stay on until December when his ruling Zanu-PF party has its congress and then he can step down - but the Zimbabwean generals want him to go now.