Key Points:

Since Zimbabwe's disputed presidential election in March, a steady stream of battered victims of President Robert Mugabe's thugs have come into the capital, Harare, telling stories of horrific intimidation in the countryside.

But in the past week the violence has arrived on the city's doorstep.

"A ring of torture camps has been established on the outskirts of Harare, and gangs of youths are marauding in the high-density suburbs [the former townships that surround the city centre]," a resident told The Independent on Sunday.

"They are stopping commuter minibuses and threatening the passengers. Many people are unable to go to work. They are being told to report every night to the camps to be taught how to vote."

Even in Harare's relatively prosperous northern suburbs, she added, there were groups of youths on the streets.

Other witnesses said gangs of militants, wearing the bandanas and scarves of Mr Mugabe's Zanu-PF party and carrying sticks and clubs, were manning makeshift roadblocks around Chitungwiza township, south of Harare, where four opposition activists were reportedly killed on Wednesday.

Party militias and "war veterans" had set up camps in suburban grassland and were frog-marching residents of Chitungwiza and other townships to political meetings ahead of Friday's presidential run-off vote.

People were told to stay indoors and avoid travelling by road at night.

The violence which broke out shortly after the election on 29 March, when the opposition leader, Morgan Tsvangirai, beat Mr Mugabe by a 6 per cent margin but narrowly failed to secure an overall majority, has escalated dramatically ahead of this week's second round.

According to independent human rights groups, 85 people have died in political violence since the first round, and tens of thousands have been driven from their homes.

In both categories, the vast majority were supporters of the opposition Movement for Democratic Change (MDC).

The worsening situation has confronted Mr Tsvangirai and the MDC with an agonising decision this weekend n whether to press on with their campaign in the face of ever-mounting intimidation and bloodshed, or to withdraw and cede victory to Mr Mugabe.

The party is taking soundings from its provincial organisations around the country, and is due to announce its decision tomorrow.

But the MDC spokesman, Nelson Chamisa, admitted that "differences of opinion" over strategy had surfaced at a meeting of the leadership in Harare.

If conditions did not change, the vote would be a "charade", Mr Chamisa told the BBC.

"Some areas are inaccessible," he said.

"People are being abducted at night. Our grassroots activists are being subjected to terror. Some of them are staying in the bushes and mountains to avoid pro-government militias."

After the March poll, in which the ruling party lost its majority in the House of Assembly to the MDC, government supporters focused their intimidation on former Zanu-PF strongholds in the rural provinces of Mashonaland, in the north and north-east of Zimbabwe, and to a lesser extent in Manicaland and Masvingo, in the east and south respectively.

Combined forces of police, soldiers, youth militia and "war veterans" sealed off areas and forced villagers to go to political meetings at which those who were unable to chant Zanu-PF slogans were savagely beaten.

In at least one case, MDC election workers were beaten to death in front of their relatives and neighbours.

The MDC's gains in March were made despite low turnouts in the cities, where voters stayed away because of cynicism about the possibility of change through the ballot box.

But even amid the reports of violent oppression in rural areas, Harare and the second city, Bulawayo, both opposition strongholds, were largely quiet.

That is changing, however, as Mr Mugabe's supporters focus on opposition calculations that a high turnout in the cities could more than make up for the loss of votes in the countryside.

One human rights group said it was investigating a report that 14 bodies had been found in a single day in the townships around Harare.

Another group, Doctors for Human Rights, said the body of a school headmaster had been found in Mutoko district, north-east of the capital, with one eye removed and his genitals severed.

The burned body of another, the wife of an opposition local council official south-west of Harare, was found with both feet and a hand removed.

While lower-ranking MDC officials face violence and possible death, Mr Tsvangirai has been subjected to constant harassment as he tries to campaign.

He has been detained at least five times by the police, and cannot transmit his message in the media.

The party's secretary-general, Tendai Biti, was immediately arrested on his return from South Africa and charged with treason, which potentially carries the death penalty.

On Friday, the party's lawyers failed in an attempt to secure his release.

A magistrate ruled that he had a case to answer and that he should remain in custody until another hearing on 7 July, while police "continue their investigations".

Mr Mugabe says, however, that the opposition is lying about political violence to justify claims that the poll will not be free and fair.

This was "a damn lie", he told a rally in Bulawayo on Friday.

But in the same speech he said: "We will never allow an event like an election to reverse our independence, our sovereignty. Only God who appointed me will remove me n not the MDC, not the British."

Others in his circle have blamed the MDC for the violence, the latest being Zimbabwe's powerful police chief, Augustine Chihuri.

"I wish to put the record straight on the political violence in Zimbabwe," the state-owned Herald newspaper quoted him as saying.

"It is without doubt that between the two political parties ... MDC-T [Tsvangirai's faction of the MDC] is the main culprit."

The police were on high alert and deployed round the country, he said, adding: "Violence will not be treated with kid gloves."

In another sign that Zanu-PF is leaving nothing to chance, the Zimbabwe Election Support Network, which had nearly 9,000 observers in the March election, said it had received invitations for only 500 this time.

Several members of the network, as well as the official Zimbabwe Election Commission, were arrested in the wake of the first round as the authorities sought scapegoats for Zanu-PF's poor performance.

The only foreign observers being allowed in for the second round are 380 monitors from the Southern African Development Community (SADC), which in March endorsed the poll as fair even before the presidential result was announced n in the event it was delayed for nearly five weeks.

But the blatant disregard for the electorate's verdict, and the growing violence since the first round, have brought public expressions of concern not only from the likes of the British Prime Minister, Gordon Brown, but even from Mr Mugabe's staunchest African allies.

Yesterday, Mr Brown demanded a halt to the violence, access for local and international monitors, and a UN investigation of human rights abuses.

More significantly, however, Angola's veteran leader, Jose Eduardo dos Santos, urged his fellow President to "embrace a spirit of tolerance and respect for democratic norms" and bring a halt to the intimidation and violence.

The appeal carried particular force, coming from an old liberation fighter who has been in power nearly 30 years, just outstripping Mr Mugabe himself.

Tanzania's Foreign Minister, Bernard Membe, also said that violence appeared to be "escalating throughout Zimbabwe".

SADC's designated mediator, South Africa's President Thabo Mbeki, appears all the more isolated as he maintains his public silence on Zimbabwe.

During an unscheduled visit to Harare last week, he met both Mr Mugabe and Mr Tsvangirai, apparently still trying to urge them to form a government of national unity.

However, since each refuses to work under the other, this tactic is unlikely to be a means of avoiding an even greater explosion of violence on and around polling day.

"It is so obvious, now that the election is not going to be free and fair, that the best strategy for the MDC would be to put pressure on African leaders," said one political analyst.

"If the party decides on its own to pull out of the election, it will hand victory by default to Mugabe.

But if does so with the explicit support of SADC, it will put pressure on Zimbabwe's neighbours to call for a postponement of the poll until safeguards can be put in place."