The two leaders will represent the 15-nation SADC bloc of which their countries are the leading members.
PIC: Angolan President Joao Lourenco
POLITICS | ZIMBABWE CRISIS
Angolan President Joao Lourenco said he and South African President Jacob Zuma would fly to Zimbabwe on Wednesday following talks between regional leaders on the crisis engulfing the country.
"(South African) President Jacob Zuma and I have agreed to visit Harare tomorrow," Angolan President Joao Lourenco told journalists Tuesday after a meeting of the southern African regional bloc in Luanda.
The two leaders will represent the 15-nation Southern African Development Community (SADC) bloc of which their countries are the leading members.
SADC has sought to broker an end to the instability triggered when Zimbabwe's army took over the country after President Robert Mugabe sacked his vice president and cleared the way for his wife Grace to succeed him.
The crisis summit "noted with great concern the unfolding political situation in... Zimbabwe", SADC said in a statement.
The announcement that the two presidents would take direct control of efforts to negotiate a settlement came after Zimbabwe's parliament began debating a motion that could eventually lead to Mugabe's impeachment.
Ousted vice president Emmerson Mnangagwa also said on Tuesday that he would return to Zimbabwe if his safety was guaranteed.
Meanwhile, Zimbabwe's parliament has began debating impeachment proceedings against President Robert Mugabe, the country's sole leader since independence 37 years ago.
Lawmakers began the historic impeachment debate shortly after ousted vice president Emmerson Mnangagwa, who could be the country's next leader, told the 93-year-old Mugabe to step down.
Mnangagwa, formerly one of Mugabe's closest allies, said in a statement that Zimbabweans had "clearly demonstrated without violence their insatiable desire" for Mugabe to resign.
"It is my appeal to President Mugabe that he should take heed of this clarion call," he said.
Parliament speaker Jacob Mubenda authorised a joint session of the House of Assembly and the Senate to debate a motion to impeach the man who is the only leader most Zimbabweans have ever known.
"This motion is unprecedented in the history of post-independence Zimbabwe," he declared.
The parliamentary procedure needed to remove Mugabe is long and complex. Legislators decided to postpone the sitting until 1430 GMT and to move to a larger venue.
There were tense protests outside parliament as hundreds of demonstrators -- from rival political parties -- shouted for Mugabe to go.
Activists hung brightly coloured postcards with political demands on lines strung between trees in a park near to parliament.
"Rename Robert Mugabe Road" said one, "free elections, no to police brutality" said another.
Morgan Tsvangirai, leader of the main opposition Movement for Democratic Change, said between the sessions that his party supports impeaching the president.
A bubbling factional squabble over the presidential succession erupted two weeks ago when Mugabe fired Mnangagwa.
The dismissal put Mugabe's wife Grace in prime position to succeed her ageing husband, prompting the military to step in to block her path to the presidency.
After Mnangagwa fled abroad, the army took over the country and placed Mugabe under house arrest -- provoking amazement and delight among many Zimbabweans as his autocratic reign appeared close to an end.
'Smell the coffee'
Mugabe suffered further humiliation on Tuesday when almost no government ministers heeded his call to attend a cabinet meeting at his State House residence, official media reported.
On Saturday, Zimbabweans attended huge, peaceful anti-Mugabe marches that would have been brutally repressed just weeks ago.
The influential war veterans' association on Tuesday threatened further protest action if Mugabe clung on.
"Smell the coffee -- your time is gone," War Veterans' association chairman Chris Mutsvangwa said.
In Luanda, the 15-nation Southern African Development Community (SADC) announced it was sending two high-powered envoys to Zimbabwe -- Angolan President Joao Lourenco and South African President Jacob Zuma.
Zuma has particular clout, both as SADC's current chair and as president of Zimbabwe's powerful neighbour.
SADC's intervention came after army chief Constantino Chiwenga told reporters late Monday that progress had been made in talks towards an apparent exit deal for Mugabe, the world's oldest head of state.
He also called for patience and calm after Zimbabweans were stunned to see the president declaring in a TV address on Sunday that he was still in power.
Mugabe is feted in parts of Africa as the continent's last surviving independence leader, having played a key role in the liberation struggle and becoming prime minister in 1980 on a wave of goodwill.
His reputation was swiftly tarnished, however, by authoritarianism, rights abuses and economic policies.
His rule has been defined by economic collapse and international isolation.
Despite his fragile health, Mugabe had previously said he would stand in elections next year that could have kept him in power until he was nearly 100 years old.
Mugabe's wife Grace, 52, has not been seen since the takeover.
We have the numbers
Chris Vandome, an analyst at Chatham House, a London-based think-tank, warned of the rising risk of public unrest.
"The longer this goes on for, the more the likelihood of violence increases," Vandome told AFP.
Legal experts say impeachment could take weeks and be subject to court appeals.
Mugabe is thought to be battling to delay his exit in order to secure a deal that would guarantee protection for him and his family.
The army insists it has not carried out a coup, but rather an operation to arrest allegedly corrupt supporters around the Mugabe family.
"It might take days and weeks, but Mugabe is on his way out," said Charles Muramba, a 46-year-old bus driver in Harare.