In recent weeks, party activists have been burned alive or have turned up dead after being spirited away in trucks, the Movement for Democratic Change said. The party's rallies have been banned and police have blocked campaign stops.

The violence, campaign restrictions and the arrest of a top opposition leader have raised concerns that the election next Friday will not be free and fair, leading some to wonder whether the vote should be scrapped in favor of a power-sharing arrangement.

The party of opposition presidential candidate Morgan Tsvangirai said more than 60 of its activists have been killed in recent weeks. Independent human-rights activists have implicated police, soldiers and Mugabe party militants in the violence.

Amnesty International said yesterday that 12 bodies had been found across the country and that most of the victims showed signs of torture. The London-based rights group said the victims appeared to have been abducted by supporters of Mugabe's ZANU-PF party.

In one of the worst single attacks, four activists were abducted in Chitungwiza, south of the capital, and assaulted with iron bars, clubs and guns, opposition spokesman Nelson Chamisa said. The victims were taken away by militias chanting slogans of Mugabe's party, witnesses said, and the bodies were found yesterday.

At the United Nations, U.S. Secretary of State Condoleezza Rice cited "great international concern" that Zimbabwe is incapable of holding a fair presidential election runoff, and urged the U.N. Security Council to intervene.

Rice, who called the violence "horrifying and intolerable," is leading a push to put Zimbabwe's election on the council's agenda this month, which could require a vote if enough members oppose it.

Mugabe has denied being responsible for the violence - but also threatened to return the country to war if he does not win the runoff.

In Harare, residents reported gangs of militants forcing maids and their family members to attend meetings known as a pungwe, a colloquial term for all-night political indoctrination used by militants since the independence war that swept Mugabe to power in 1980. Among those killed in the violence was the wife of opposition mayor-elect of Harare.

South African President Thabo Mbeki held talks with Tsvangirai and Mugabe in Zimbabwe on Wednesday, but canceled a news conference yesterday "due to unforeseen circumstances." South African media reported that Mbeki, who has refused to publicly rebuke Mugabe, was trying to persuade the two men to form a unity government.

The idea has been raised before, but Tsvangirai refuses to share power, while Mugabe insists on leading any coalition government.

Also yesterday, the Zimbabwean opposition party's No. 2 official, Tendai Biti, was brought back to court for a hearing a week after he was arrested. Police accused him of treason and publishing false statements among other offenses. "It's all part of harassment," Tsvangirai told reporters.