HARARE, Zimbabwe - Zimbabwe's opposition leader called on his supporters Friday to challenge President Robert Mugabe's rule in next week's runoff election despite a "wave of brutality" he says the government has unleashed.

Even as Morgan Tsvangirai urged Zimbabweans to have the courage to vote in the face of a violent crackdown, a judge ordered the No. 2 opposition leader held on treason and other charges until after the election.

"The wave of brutality being inflicted upon our people is reminiscent of the worst days of" white rule, Tsvangirai said in an e-mail, one of the few ways he has of reaching voters.

The opposition leader's attempts to tour the country have regularly been stymied by police at road blocks, and the state-controlled media here all but ignore him.

Independent human rights activists have accused Mugabe of deploying police, soldiers and party militants in attacks on the opposition meant to ensure he defeats Tsvangirai in the runoff. The opposition says more than 60 of its activists alone have been killed, and the international community has become so concerned at the violence that some leaders have suggested the runoff be canceled.

Tsvangirai's Movement for Democratic Change says the treason case against its secretary-general, Tendai Biti, is also part of a government plot to undermine it before the election. After hearing two days of arguments from prosecutors and defense lawyers, Magistrate Mishrod Guvamombe ruled Friday that there were grounds to believe Biti had committed an offense and ordered him held until another hearing set for July 7.

Biti was formally charged Thursday with treason, which can carry the death penalty, publishing false statements, insulting the president and another charge related to interfering with the military -- police said Biti had spoken to generals about which military figures should step down if his party were to come to power.

The charge of making false statements was based on Biti's announcement -- before official results were released -- that Tsvangirai won the first round of presidential voting March 29. Under the law, only electoral officials can release results, but the government delayed announcing the results for more than five weeks.

Opposition leader Tsvangirai claims he won the first round vote outright. Official results indicate he came in first in a field of four, but failed to win the 50 percent plus one vote necessary to avoid a second round against Mugabe.

"Help us to remind our people that they are winners. That their courageous decision on 29 March was not in vain," Tsvangirai said. "Help us encourage them to vote again for change on 27 June. Help us to protect them from the regime's attempt to destroy their hope.

"On 27 June, let's finish it!"

Mugabe, Zimbabwe's head of government since 1980, was lauded early in his rule for campaigning for racial reconciliation. But in recent years, he has been accused of ruining the economy and holding onto power through fraud and intimidation.

The economic slide of what was once the region's breadbasket has been blamed on the collapse of the key agriculture sector after often-violent seizures of farmland from whites.

Mugabe claimed he ordered the seizures, begun in 2002, to benefit poor blacks. But many of the farms instead went to his loyalists.

According to a draft EU statement obtained by The Associated Press, European Union leaders will threaten Zimbabwe's authorities with more sanctions Friday amid reports of escalating violence against the opposition.

EU nations already have suspended development aid and imposed arms embargo against Zimbabwe as well as an assets freeze and travel ban against Mugabe and 125 other top government officials. Those sanctions first were imposed in 2002 to protest human rights violations in Zimbabwe and Mugabe's dictatorial rule.