The opposition has accused President Robert Mugabe of orchestrating delays in the election process and assaults on its supporters in a bid to extend his 28-year rule.

Opposition leader Morgan Tsvangirai, who won the first round, has yet to decide whether he will contest a run-off.

By law, the Zimbabwe Electoral Commission (ZEC) is supposed to set the date within 21 days of the result. But it has the power to extend the period and political observers believe a 40-day period is likely.

Utoile Silaigwana, ZEC's deputy chief elections officer, would not be drawn on whether it planned to extend the date.

"The commission will soon meet over this matter," he said.

The opposition Movement for Democratic Change is still considering whether to contest the second round, rejecting official results of the March 29 election showing Tsvangirai won with less than the outright majority needed to defeat Mugabe.

Mugabe, 84, has accepted the official results, and the ruling ZANU-PF says he will be its candidate on the second ballot.

The MDC is under growing pressure to announce its intentions. Tsvangirai is in a tight spot. If he does not stand, it would automatically hand victory to his old foe Mugabe.

MILITIAS

The opposition, Western governments and human rights groups have accused Mugabe of unleashing militias to scare Zimbabweans into backing him in the run-off. The government denies the allegation and says the MDC is behind political violence.

The MDC says at least 20 of its supporters have been killed and more than 1,000 homes burnt or destroyed since the election.

Teachers, who make up the bulk of polling officers, have been targets of a violent campaign to influence the outcome of the vote, a union said.

The Progressive Teachers' Union of Zimbabwe (PTUZ) said in a statement over 2,740 teachers had been targeted.

It said 133 teachers had been assaulted -- with 23 of them hospitalised -- and four houses belonging to teachers torched. A total of 31 schools had been completely deserted by teachers, PTUZ said.

Tendai Chikowore, head of Zimbabwe's main teachers' union, the Zimbabwe Teachers' Association (ZIMTA), said more and more teachers were victims of the campaign.

"We continue to receive reports every day, from our members all over the country that they are being beaten and threatened," he said.

MDC officials said party leaders were hammering out conditions they would demand for Tsvangirai's participation in a second round -- including a strong international observer mission and the speedy release of results.

The opposition says the month-long delay in announcing the last result allowed the outcome to be rigged. The official result showed Tsvangirai won 47.9 percent of the vote to Mugabe's 43.2 percent.