The United States and Europe are lining up behind Zimbabwe's main opposition candidate, who is claiming election victory over President Robert Mugabe.

Morgan Tsvangirai said during a press conference Tuesday that voters have given birth to a new nation by siding with his Movement for Democratic Change party, but he denied his party has begun any transition talks with Mugabe, who has ruled the country for 28 years.

Tsvangirai said he would not hold discussions with Mugabe's ruling ZANU-PF party before the official announcement of the final election results.

In Washington, the White House indicated it believed the opposition had won, according to the Associated Press.

"It's clear the people of Zimbabwe have voted for change," said Gordon Johndroe, spokesman for the National Security Council. "It's time for the Zimbabwean Electoral Commission to confirm the results we have all seen from the local polling stations and respected NGOs."

The European Union said it wants Mugabe to step down to spare his nation political turmoil.

"If Mr. Mugabe continues, there will be a coup d'etat," said Slovenian Foreign Minister Dimitri Rupel, whose country holds the EU presidency. He said he hoped Mugabe "is on his way out."

British Prime Minister Gordon Brown called for the immediate release of election results.

Tsvangirai claimed to have eclipsed the 50 percent simple majority needed to avoid a runoff, The Associated Press reported.

He condemned the Zimbabwe Electoral Commission for not taking greater haste in releasing the results of Saturday's presidential race.

"Our country is on a precipice, on a cliff edge," Tsvangirai told the AP. "There are no discussions, Let's wait for ZEC to complete it's work, then we can discuss the circumstances that will affect the people."

Tsvangirai lamented Zimbabwe's conditions under Mugabe during the press conference.

"For years we have trod a journey of hunger, pain, torture and brutality," he said. "Today we face a new challenge of governing and rehabilitating our beloved country, the challenge of giving birth to a new Zimbabwe founded on restoration not retribution, on love not war."

There were conflicting reports over whether the main Zimbabwean opposition party is holding talks with advisers to President Mugabe about the possibility of Zimbabwe's longtime leader relinquishing power.

The secretary-general of Tsvangirai's party, Tendai Biti, dismissed the reports, saying "it's rubbish."

Zimbabwe's opposition MDC party denied reports it was in negotiations with the governing ZANU-PF on a handover of power by Mugabe, Reuters reports.

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MDC spokesman in London Hebson Makuvise vehemently denied a report that talks are underway between opposition and ruling party officials, the BBC reports.

"There is nothing like that," he told the BBC.

But the denial was in conflict with other reports which suggested the talks were taking place.

A source close to the state's electoral commission told Sky News Mugabe has been told he is a long way behind Morgan Tsvangirai in preliminary results of presidential elections.

His advisers fear there could be an uprising if Mugabe were declared the winner, the anonymous source told Sky News.

Several diplomats have confirmed they have heard similar stories, but could not corroborate the information.

A businessman close to the electoral commission and a lawyer close to the opposition told The Associated Press on Tuesday that advisers to both men were discussing a "transitional arrangement."

Both spoke on condition of anonymity because of the sensitivity of the issue.

Martin Rupiya, a military analyst at South Africa's Institute for Strategic Studies and a former lieutenant-colonel in the Zimbabwe army, said he had heard of the military's involvement in negotiations for Mugabe to step down.

The election outcome "has compelled the military, the hawkish wing and the other moderate, to begin to reconsider accommodating the opposition," he said. "Because of the nature of the wins they have been forced to reassess."

Independent observers say trends indicate Tsvangirai won the most votes in the presidential race, but not enough to avoid a runoff — a prospect that could be humiliating to the 84-year-old president.

No returns from the presidential vote have been made public, fueling fears of rigging. Mugabe has been accused of stealing past elections, though that was before Zimbabwe's economy collapsed and leading members of his own party openly defied him.

The businessman said Zimbabwe's security chiefs have told the Electoral Commission to issue results portraying a close race, to prevent celebrations that could ignite violence.

The commission has released results for 142 of the 210 parliamentary seats — giving Tsvangirai's Movement for Democratic Change 72 seats, including five for a breakaway faction, and 70 for Mugabe's party.

John Makumbe, a political scientist at the University of Zimbabwe, said he had learned from military sources that they would honor the results of the elections. The security chiefs last week warned they would not serve anybody but Mugabe and would not tolerate an opposition victory.

Tsvangirai on Tuesday postponed his first public statement since the elections until later in the day. His spokesman George Shibotshiwe said that was because the opposition party had received "a tremendous breakthrough in the numbers coming in" from the elections.

The opposition already has claimed victory in the elections based on results posted outside polling stations, including in several rural strongholds of Mugabe. The initiative to display the results on voting station doors was part of an agreement between the parties negotiated by South African President Thabo Mbeki, and could make it more difficult to cheat.

The European Union said it wants Mugabe to step down to spare his nation political turmoil.

"If Mr. Mugabe continues, there will be a coup d'etat," said Slovenian Foreign Minister Dimitri Rupel, whose country holds the EU presidency. He said he hoped Mugabe "is on his way out."

British Prime Minister Gordon Brown called for the immediate release of election results.

"Results should be published immediately and the elections must be seen to be fair," Brown told reporters in London. "It's very important that the democratic rights of the Zimbabwe people be respected and upheld and recognized."

The Netherlands hailed the possibility of an opposition victory.

"I get the impression that the Zimbabweans have voted for change and democratic forces have the upper hand," said Dutch Foreign Minister Maxime Verhagen. "Now, finally, the people of Zimbabwe have the prospect of a better life."

Tsvangirai has vowed not to entertain an alliance with Mugabe but has said previously that he is ready to negotiate an exit package for Zimbabwe's ruler for 28 years. He also has said that Mugabe should be tried for human rights abuses, possibly in an international court.

It appeared Mugabe was persuaded into talks by the possibility of a runoff presidential race, which the businessman said he would find too demeaning.

The Zimbabwe Election Support Network, a coalition of 38 Zimbabwe civil society organizations, said its random representative sample of polling stations showed Tsvangirai won just over 49 percent of the vote and Mugabe 42 percent. Simba Makoni, a former Mugabe loyalist, trailed at about 8 percent.

A presidential candidate needs at least 50 percent plus one vote to avoid a runoff.

Mugabe would have to weigh the concerns of those who have profited from his patronage, a group that includes top military leaders, party officials and business people. They receive mining concessions, construction contracts and preferential licenses to run transport companies and other businesses.

Marwick Khumalo, head of the Pan-African Parliament observer mission, told South African radio Tuesday that leading members of Mugabe's party were contemplating defeat with trepidation.

"I was talking to some of the big wigs in the ruling party and they also are concerned about the possibility of a change of guard," Khumalo said. "ZANU-PF has actually been institutionalized in the lives of Zimbabweans, so it is not easy for anyone within the sphere of the ruling party to accept that 'Maybe we might be defeated or might have been defeated."'

Mugabe led a guerrilla movement that fought a seven-year war to end white minority rule. At independence, he was hailed for his policies of racial reconciliation and development that brought education and health to millions who had been denied those services under colonial rule. Zimbabwe's economy thrived on exports of food, minerals and tobacco.

The unraveling began when Mugabe ordered the often-violent seizures of white-owned commercial farms, ostensibly to return them to the landless black majority. Instead, Mugabe replaced a white elite with a black one, giving the farms to relatives, friends and cronies who allowed cultivated fields to be taken over by weeds. Today, a third of the population depends on imported food handouts. Another third has fled the country as economic and political refugees and 80 percent is jobless. Life expectancy has fallen from 60 to 35 years and shortages of food, medicine, water, electricity and fuel are chronic.

The economy is in dramatically worse shape than during past elections, driving other changes in Zimbabwe's political landscape. The candidacy of Makoni, a former finance secretary, drew open support from other leaders in the ruling party.

The Associated Press, Sky News, Reuters and the BBC contributed to this report.