Heavily armed riot police have been deployed in potential election flashpoints in Zimbabwe on the eve of a poll showdown between President Robert Mugabe and Prime Minister Morgan Tsvangirai that remains too close to call.

State radio said thousands of officers had been sent to the central Midlands province on Tuesday, while trucks of police carrying automatic rifles and grenade launchers patrolled in the restive Harare townships of Highfield and Mbare.

The run-down districts of the capital are hotbeds of support for Tsvangirai and were at the centre of several weeks of post-election violence in 2008, in which 200 people linked to his Movement for Democratic Change (MDC) were killed.

This year's presidential and parliamentary elections have been marked by allegations of threats and intimidation by security forces, but there have been no reports of violence.

About 6.4 million people are eligible to cast their ballots in the first round of presidential and parliamentary elections.

With no reliable opinion polls, it is hard to tell whether 61-year-old Tsvangirai will succeed in his third attempt to unseat his 89-year-old rival, who has run the southern African nation since independence from Britain in 1980.

Voter irregularities

Both the MDC and Mugabe's ZANU-PF party predict landslide victories. However, it is possible neither leading candidate will emerge an outright winner, triggering a September 11 run-off.

Mugabe's rivals have submitted what they claim is evidence of his plans to rig the vote to regional election observers.

Allies of Tsvangirai presented a sample list of about125 duplicate or questionable voters on the electoral roll to observers from the Southern African Development Community.

Speaking at a press conference in Harare on Tuesday, Mugabe said that if someone lost the competition that person should surrender to those who won it.

Al Jazeera’s Haru Mutasa, reporting from Harare, said Mugaba was confident of winning the election and believed that there will not be a power sharing deal with MDC.

“He refused to talk about succession plans or say if this is his last election” our correspondent said.

“He dismissed allegations of intimidation of people in rural areas ahead of vote. He said he did not have the power to interfere in the voting process adding that elections had always been democratic and he had never cheated.”

Given the irregularities and problems that have dogged the election process, including failure to publish an electronic voters' roll, the result is highly likely to be contested, raising the prospect of another long political stalemate.

In 2008, South Africa and other countries in the region negotiated a unity government between Mugabe and Tsvangirai to break a deadlock caused by the MDC's withdrawal from a second-round runoff because of the violence and killings.

Western election observers have been barred, leaving the task of independent oversight to 500 regional and 7,000 domestic monitors. The final results must be released within five days, but may come sooner.