Zimbabwe's opposition leader Morgan Tsvangirai rejected calls on Tuesday for a national unity government instead of a presidential runoff vote and said his party was sure to win the election despite government violence.

Tsvangirai told a news conference Zimbabwe had suffered a de facto coup and was being run by a military junta.

Some 66 supporters of his Movement for Democratic Change (MDC) had been killed since disputed March elections, he said.

Simba Makoni, a defector from the ruling ZANU-PF party and a former finance minister, said earlier the June 27 run-off between President Robert Mugabe and Tsvangirai must be called off because a free and fair vote was impossible.

"Following the announcement of the date for the run-off, no one can change that due process unless Robert Mugabe concedes defeat, or collapses. It therefore means that a government of national unity negotiated before the runoff does not arise," Tsvangirai said.

U.S. Secretary of State Rice was consulting other countries to see what practical steps could be taken by the international community to ensure a real runoff election.

"We're continuing to focus on trying to make this runoff election one that can be as free and fair as possible, that will reflect the will of the Zimbabwean people. Whether or not that can happen is an open question," U.S. State Department spokesman Sean McCormack added.

HUMAN RIGHTS WATCH

U.S.-based Human Rights Watch also said brutal intimidation and murder by Mugabe's supporters made normal campaigning impossible.

"As a people we have been exposed to state-sponsored brutality. The violence continues unabated," Tsvangirai said.

He said 3,000 MDC supporters had been injured and more than 25,000 displaced but the MDC would win even if ZANU-PF prevented them campaigning.

"As far as I am concerned I can stay home from now on until the election, Mugabe will lose. It's just a formality to go and campaign, the people have already decided."

An EU-U.S. summit in Slovenia on Tuesday called on the Zimbabwe government to end what it called state-sponsored violence and urged U.N. Secretary-General Ban Ki-moon to send monitors to deter further violence.

Makoni, who challenged Mugabe in disputed March 29 elections, told reporters in Johannesburg that 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 place," he said.

Makoni 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.

South Africa's Business Day newspaper reported on Tuesday ZANU-PF and MDC were in talks that could lead to the cancellation of the poll.

UNITY GOVERNMENT UNLIKELY

Lovemore Madhuku, chairman of Zimbabwean political pressure group National Constitutional Assembly (NCA), said a government of national unity was unlikely in the short term.

"I know that a lot of people are talking about that, but I don't see that happening in the coming months because of the polarisation between ZANU-PF and the MDC," he told Reuters.

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. Mugabe blames his foes for the bloodshed.

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 campaigning.

Business Day, quoting negotiators for both sides, said ZANU-PF and the MDC were in talks mediated by South African President Thabo Mbeki.

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). Mbeki has been widely criticised for his softly softly approach to Mugabe.

In a statement, Zimbabwe Lawyers for Human Rights said two lawyers had been forced to flee to South Africa and a third had gone into hiding over threats to their lives for handling cases involving opposition officials and activists.

"In recent weeks, the operating environment for members of the legal profession, more particularly human rights lawyers, has shrunk to the extent that it is becoming almost impossible for them, as officers of the court, to perform their professional duties and functions," it said.