Motlanthe said Mugabe and the MDC had agreed a power-sharing timeline
Zimbabwe's rival factions are committed to a power-sharing deal, South African President Kgalema Motlanthe has said.
Zanu-PF and the Movement for Democratic Change (MDC) had agreed to form a unity government next month, he said.
But the MDC said the conclusions of the summit chaired by Mr Motlanthe fell short of its expectations.
President Robert Mugabe reached a deal with MDC leader Morgan Tsvangirai last September but they could not agree who should control key government posts.
Zimbabwe is in a state of economic and social collapse, and a cholera epidemic has killed nearly 3,000 people.
After 14 hours of negotiations, leaders from the Southern African Development Community (SADC) issued a statement early on Tuesday saying the MDC had agreed to a timeline towards forming a unity government.
According to the timeline, a constitutional amendment would be passed to create the post of prime minister on 5 February, with Mr Tsvangirai being sworn in six days later.
"All the parties expressed confidence in the process and committed to implementing the agreement," said Mr Motlanthe.
But an MDC statement said the party had not agreed to the deal, and although it stopped short of rejecting the summit's conclusions outright, it said the summit resolutions "fell far short" of what the party had hoped for.
"Quite clearly, the conclusions reached as reflected in the [SADC statement] fall far short of our expectations," said the MDC
It added that the party's national council would meet this weekend to define its position.
Earlier on Monday, seven people were taken to hospital when police fired rubber bullets at several hundred people demonstrating outside the talks in Pretoria.
It was the fourth such meeting since the inconclusive elections last March.
Mr Mugabe and Mr Tsvangirai failed to resolve their differences during a meeting in Harare last week.
One analyst says those talks collapsed in "real acrimony".
The main issue of contention is over who controls key ministries and other top public posts.
President Mugabe has said he will not compromise any further and there have been reports he may ask SADC for the legitimacy to form a new government without the MDC opposition.
SADC looks powerless and has shown no willingness to impose sanctions on Zimbabwe, says the BBC's Peter Biles in Pretoria.