Morgan Tsvangirai (left) says Robert Mugabe has lost control
The second-round run-off in Zimbabwe's disputed presidential election will be held on 27 June, the government says.
Opposition leader Morgan Tsvangirai won the first round, but not by enough to avoid a run-off. President Robert Mugabe said the poll was "disastrous".
Mr Tsvangirai says he will contest the second round, after originally threatening to boycott it.
He has accused Mr Mugabe's party of vote-rigging and a campaign of violence against opposition activists.
His Movement for Democratic Change (MDC) says ruling party militias and soldiers have beaten and tortured MDC supporters in an attempt to either keep them away from the polls or intimidate them into voting for the ruling party.
Our structures went to sleep, were in deep slumber in circumstances of an all-out war
President Robert Mugabe
Mr Tsvangirai said on Friday that "violence has to cease for an election to be conducted or that election will not be legitimate".
However, he told the BBC that Mr Mugabe had lost control of the country and that the army was now in charge.
"Mugabe may be the figurehead but the people who have taken over are the military," he told the BBC's Orla Guerin.
Zimbabwe has been in political crisis since parliamentary and presidential elections on 29 March.
Axe attack
The US Ambassador to Zimbabwe, James McGee, told the BBC's Newsnight programme he had found evidence of state-sponsored political violence, including a hatchet assault on an elderly woman.
"Her two grand-sons were activists with the MDC party," he said.
Please turn on JavaScript. Media requires JavaScript to play.
"They were beaten up and then the people who beat them up found their grandmother and hit this 80-year-old woman in the head with an axe."
Mr McGee, who has been accused by state-owned media of trying to demonise Zimbabwe, said fair elections were "not possible" in the current political climate.
But Zanu-PF spokesman Bright Matonga told the BBC that the ruling party was not involved in the violence.
"Let me make it very clear that the Zimbabwe government does not support any violence - whether by MDC or Zanu-PF," he said.
Mr Mugabe told a party meeting on Friday that it should have been more prepared for the election.
"Although the presidential result did not yield an outright winner, it was indeed disastrous," he said.
"Fundamentally we went to the election completely unprepared, unorganised... Our structures went to sleep, were in deep slumber in circumstances of an all-out war."
Mr Mugabe also accused opposition followers of terrorising Zanu-PF supporters, warning that they were "playing a dangerous game".
Poll 'plot'
Despite accusing the ruling party of attacks, Mr Tsvangirai told the BBC that exploratory contacts were under way between the two sides.
Mr Tsvangirai said Zanu-PF had made "overtures" to the MDC about the possibility of a national unity government.
Please turn on JavaScript. Media requires JavaScript to play.
The BBC's Orla Guerin interviews Morgan Tsvangirai
"Nothing concrete has been put in place, but on the sidelines there may be: 'Can we talk?' at a very minimum stage," he said.
Mr Tsvangirai has been out of Zimbabwe since the first-round vote because of alleged threats to his life.
But the MDC says he will return to address a rally in Bulawayo on Sunday.
The MDC says 35 people have been killed since the relatively peaceful first round and thousands displaced and tortured.
The run-off was due to be held by 23 May - 21 days after the results of the first round were announced - but the government then issued an emergency law allowing it 90 days to organise the new poll.
Bookmark with:
What are these?