Zimbabwe's long-time President Robert Mugabe is reportedly refusing to step down immediately, despite growing calls for his resignation.
The 93-year-old was put under house arrest during a military takeover on Wednesday, amid a power struggle over who would succeed him.
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, signalling that he favoured 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 legitimise 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.
Mr Mugabe (second right) under house arrest, posing alongside Zimbabwe Defence Forces Commander General Constantino Chiwenga (right) Mr Mugabe (second right) under house arrest, posing alongside Zimbabwe Defence Forces Commander General Constantino Chiwenga (right) What do South Africa and the region want?
South Africa is hosting millions of Zimbabweans who fled after the country's economy crashed in 2008. It has a special interest in seeing stability restored.
South African Defence Minister Nosiviwe Maphisa-Nqakula and State Security Minister Bongani Bongo are the envoys meeting Mr Mugabe on behalf of Sadc, which South Africa currently leads.
Sadc also held a meeting in neighbouring Botswana and called for a regional summit to discuss the crisis. They urged Zimbabwe to "settle the political challenges through peaceful means," the AFP news agency reports.
The African Union said it would not accept a military seizure of power. AU head and Guinea President Alpha Condé said he was "inviting the army to return to its barracks and return to constitutional order".
And Zimbabwe's opposition?
Mr Tsvangirai, head of the Movement for Democratic Change-Tsvangirai (MDC-T) party and the main opposition leader in Zimbabwe, said Mr Mugabe's immediate resignation must be part of a "negotiated all-inclusive transitional mechanism".
He said this should lead to "comprehensive reforms for free and fair elections to be held" - views echoed by another opposition leader Tendai Biti.
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