Zimbabwe is too violent to hold a presidential run-off, the head of a South African observer mission says.
"We have seen it, there are people in hospital who said they have been tortured," said Kingsley Mamabolo.
The head of the Zimbabwe Electoral Commission has reportedly said the run-off could be delayed by up to a year.
No date has been set for the second round between President Robert Mugabe and Morgan Tsvangirai, which should be 21 days after the official results.
These, announced last Friday, said that Mr Tsvangirai gained more votes than Mr Mugabe but not the 50% needed to be declared the winner.
Mr Tsvangirai, however, says the results were fixed and insists that he did pass the 50% threshold.
He has not said whether he would take part in a run-off, citing fraud and alleged state-sponsored violence against his supporters.
Mr Mamabolo did not say who was behind the recent violence but pointed out that both side was accusing the other, so there was no doubt whether it was happening.
"You cannot have the next round taking place in this atmosphere; it will not be helpful," he said.
Up to 40,000 farm-workers and their families have fled their homes because of the violence, a trade union official has said.
"They have been attacked by a group of militias wearing army uniforms," said Gertrude Hambira, General Secretary of the General Agriculture and Plantation Workers Union of Zimbabwe.
"They have been accused of voting for the opposition. Most of them are either on the roadside or sheltering at some farms."
Much of the political violence in recent years has been on white-owned farms but all but 400 of these have been seized by the state and redistributed.
Church leaders in the western Matabeleland province say they have had to stop prayer meetings after some priests were abducted and tortured by ruling party supporters.
Meanwhile, a photographer for the Reuters news agency has been arrested for using a satellite phone, the agency says.
Mr Mamabolo added that South African President Thabo Mbeki had sent a fact-finding mission to Zimbabwe.
Mr Mbeki is the lead mediator in the Zimbabwe crisis, although Mr Tsvangirai has said he wants a replacement.
'Peace and transparency'
Meanwhile, the head of the Pan-African Parliament observer team, Marwick Khumalo, said Zimbabwe Electoral Commission chairman George Chiweshe had told him that the run-off could be delayed by up to a year.
"He told me it was not possible to organise an election within the 21 days required by the constitution," said Mr Khumalo, a Swaziland MP.
"He said the election would be organised within the shortest possible time and this would not be longer than 12 months."
Mr Tsvangirai has called for international observers to be sent to monitor the run-off - a call backed up by UN Secretary General Ban Ki-moon.
Western observers were banned from the first round by the Zimbabwe government, which accused them of bias, after they said there had been fraud in previous elections.
African Union head Jean Ping has told the BBC that the continental body would send extra observers to Zimbabwe for the run-off.
He was speaking after meeting President Mugabe, as well as the leaders of Zambia and South Africa.
"The assurances given to me were that the second round would take place in peace and transparency," he said.
If Mr Tsvangirai does not contest the run-off, Mr Mugabe would automatically win.
But MDC Secretary General Tendai Biti says they had other options, without elaborating.
"If Mugabe thinks he's going to get a default presidency, that will be over our dead bodies," Mr Biti said.
Mr Tsvangirai's Movement for Democratic Change says at least 25 of its supporters have been killed since the relatively peaceful first round on 29 March.
It says many hundreds have been forced from their homes in rural areas in a deliberate strategy to stop it campaigning effectively for the run-off.
But police and officials from Mr Mugabe's Zanu-PF party have accused the MDC of staging attacks, while accusing the MDC of exaggerating the scale of the violence.
