Initial word of the agreement came from MDC founder Morgan Tsvangirai who told reporters that "I can say we have an agreement" as he left the negotiations venue at the Rainbow Towers Hotel in Harare around 9 p.m.
It is believed that Tsvangirai will become Zimbabwean prime minister under the deal in cooperation with President Robert Mugabe. The agreement will presumably assign a senior role to rival MDC formation leader Arthur Mutambara.
President Mbeki confirmed a short time later that the negotiators and the principals - Mr. Mugabe, Tsvangirai and Mutambara - had come to an agreement.
"An agreement has been reached about all of the matters set on the agenda," Mr. Mbeki told a news conference. "There will be a formal signing ceremony on Monday, this Monday, at 10 o'clock here in Harare, at which point the document, which will be signed then by the political leaders of Zimbabwe, will be released."
Mr. Mbeki added: "They have all of them endorsed the document tonight, signed it, but the document as I have indicated will be released to the public on Monday at that ceremony at 10 o'clock, which will be attended by leaders of the region and the continent to express their support for the agreement that has been arrived at."
The agreement caps an intense and often traumatic period for Zimbabwe from the March elections which gave the MDC its parliamentary majority but by a disputed official count failed to deliver to Tsvangirai an absolute majority in the presidential race.
The March first round of elections was soon followed by a wave of political violence that most observers agreed was mainly perpetrated by loyalists of Mr. Mugabe's defeated ZANU-PF party against officials and members of Tsvangirai's MDC formation.
Mounting violence led Tsvangirai to pull out of a June 27 run-off election, in which Mr. Mugabe, unopposed, claimed victory amid international opprobrium.
African and international diplomacy led to the initiation of the power-sharing talks in the aim of forging a national unity government along lines similar to that formed by Kenyan politicians following a harrowing post-election period in that country in early 2008.
Negotiators for Tsvangirai's MDC formation, that of rival Arthur Mutambara, and ZANU-PF had been in talks off and on since late July, and most recently since Monday in Harare in the final approach to the preliminary signing of the agreement.
Earlier, the talks had appeared to be stalling again over the question of how to structure the cabinet in the proposed government of national unity.
President Mugabe fired a broadside at the MDC in remarks to traditional chiefs in Bulawayo, saying it was humiliating to negotiate with a party “sponsored by countries pushing for regime change.” He said the talks have made no real progress.
MDC negotiators were calling for a council of ministers chaired by Tsvangirai in addition to the cabinet, which president Mugabe would chair.
The proposed council of ministers would
include two deputy prime ministers as well as the two vice presidents - currently Joseph Msika and Joyce Mujuru.
The council of ministers would debate and formulate government policy and oversee implementation. Mugabe would remain chairman of the cabinet, which would review the council’s work. Sources privy to the talks said Tsvangirai backed the new arrangement but Mugabe rejected it.
The fate of MDC formation leader Arthur Mutambara remained unclear - he sought the post of deputy prime minister.
Correspondent Thomas Chiripasi of VOA's Studio 7 for Zimbabwe, at the talks venue, told VOA reporter Blessing Zulu of VOA that the talks started late as Mugabe had asked for time to attend the chiefs Council meeting in Bulawayo.
For perspective reporter Zulu turned to lawyer and political analyst Brian Kagoro, who says the call for a council of ministers is complicated.
Meanwhile, SADC executive secretary Tomaz Salamao told VOA that leaders of the SADC troika led by Swaziland were on standby in Mbambane. Salamao said MR. Mbeki had asked for more time to try and hammer a deal before flying to the troika meeting.
Former United Nations Secretary General Kofi Annan slammed the African Union Thursday for not confirming the MDC victory in Zimbabwe's March elections.
"I am disappointed in the African Union," Annan told a conference at the German Foreign Ministry in Berlin."The African Union should have endorsed the results and said to Mugabe: you are not a legally elected president."
offered to mediate to resolve the standoff as he did earlier this year in Kenya
after an election that the opposition charged was rigged by President Mwai
Kibaki. But Harare has told Annan to back off.