|Robert Mugabe pictured for first time since Zimbabwe's military takeover|
The military said on Friday it was "engaging" with Mr. Mugabe.
It also said it had been arresting "criminals" around the president, but gave no names.
Several senior officials are said to have been detained since Wednesday.
"Others are still at large," the military said.
In a televised statement, the military said it would advise the nation on the outcome of talks with Mr. Mugabe "as soon as possible".
Opposition leader Morgan Tsvangirai said it was "in the interests of the people" that Mr. Mugabe "resign... immediately".
The army moved in after Mr. Mugabe last week sacked Vice-President Emmerson Mnangagwa, signaling that he favored his wife Grace Mugabe to take over his Zanu-PF party and thus the presidency.
The BBC's Andrew Harding, in Zimbabwe, says that if President Mugabe can be persuaded to step down officially it could help legitimize the military's dramatic intervention.
On the streets, it is hard to find anyone who wants Mr. Mugabe to stay on, our correspondent adds, but negotiating the manner of his departure and some sort of transitional agreement to follow could take some time.
Alongside them was Father Fidelis Mukonori, a Roman Catholic priest known to Mr. Mugabe for years, who has been brought in to mediate. Sources close to the talks say Mr. Mugabe - who has been in control of Zimbabwe since it threw off white minority rule in 1980 - is refusing to stand down voluntarily before next year's planned elections.
"I think he is trying to buy time," one source close to the army leadership told the AFP news agency.
Some observers suggest that Mr. Mugabe may be trying to seek guarantees of safety for himself and his family before stepping aside.
Zanu-PF officials had earlier suggested Mr. Mugabe could remain nominally in power until the party congress in December, when Mr. Mnangagwa would be formally installed as party and national leader.
|President Robert Mugabe meets an army chief and South African envoys|
Many Zimbabweans almost instantly warmed to the military's move to take control of the country, and confine President Mugabe to his official residence.
"The military has done a good thing," says one bookseller. "They will ensure we get a transitional government."
He is firmly convinced that Mr. Mugabe's 37-year rule is coming to an end.
There has been a sudden change of tone in the country, and the sense is that many Zimbabweans have been yearning for change.
Any change, it seems, would do.