Makoni's statement came after a similar call by U.S.-based Human Rights Watch, which said brutal intimidation and murder by supporters of President Robert Mugabe made normal campaigning impossible for the June 27 poll.

An EU-U.S. summit in Slovenia on Tuesday called on the Zimbabwe government "immediately to cease the state-sponsored violence and intimidation against its people."

It urged U.N. Secretary-General Ban Ki-moon to send monitors to Zimbabwe to deter further violence.

Makoni, who challenged Mugabe in disputed March 29 elections, told reporters in Johannesburg that opposition leader Morgan Tsvangirai must negotiate a five-year transitional government.

"Normal political conduct and behaviour is not possible in the circumstances within Zimbabwe at the moment. I don't believe we can have free elections under these circumstances that's why we are suggesting that the run-off will not take place," he said.

A South African newspaper reported on Tuesday that ZANU-PF and Tsvangirai's Movement for Democratic Change (MDC) were in crisis talks that could lead to cancellation of the poll.

Makoni, a former finance minister, came a distant third in the March election in which Tsvangirai beat Mugabe but failed to reach the absolute majority needed to avoid a second round.

Human Rights Watch said on Monday a free and fair poll was impossible because of a systematic campaign of murder and torture unleashed by ZANU-PF in which at least 36 people had died. Some 2,000 people were victims of violence.

MUGABE BLAMES OPPOSITION

Mugabe blames his foes for the violence.

Jacob Zuma, leader of the ruling party in Zimbabwe's powerful neighbour South Africa, said during a tour of India on Tuesday that he was alarmed and anxious about the reports of violence and called on ZANU-PF to ensure free political activity.

South Africa's Business Day newspaper, quoting negotiators for both sides, said on Tuesday:

"ZANU-PF and the opposition ... are engaged in 11th hour talks -- mediated by President Thabo Mbeki -- to salvage a solution to the political stalemate, which may include cancelling a proposed presidential run-off election."

Business Day quoted the negotiators as saying the run-off might be too "dicey".

They were looking at various options including a national unity government led by Mugabe, with Tsvangirai as prime minister -- similar to the solution found for Kenya's bloody crisis earlier this year.

This idea was previously rejected by the MDC.

Makoni said he was involved in consultations between the two sides but they could not be described as negotiations. He called for this process to be accelerated.

Mbeki spokesman Mukoni Ratshitanga said he was unaware of the talks.

Zuma, who has been outspoken about the Zimbabwe crisis, is frontrunner to succeed Mbeki next year after toppling him as leader of the ruling African National Congress (ANC). The latter has been widely criticised for his softly softly approach to Mugabe.