Zimbabwean President Robert Mugabe's opponents joined together on Thursday and accused him of plotting to rig Saturday's election, the toughest battle of his 28 years in power.

After Mugabe handed out hundreds of cars to doctors in what critics say is a vote buying campaign, he faced fresh accusations that he would steal the poll.

Mugabe has vowed to crush old rival Morgan Tsvangirai and ruling ZANU-PF party defector Simba Makoni. Both accuse Mugabe of wrecking what was once one of Africa's most promising economies.

Makoni and the two factions of the opposition Movement for Democratic Change (MDC) said they had more evidence of planned ballot rigging and believed Mugabe was planning to declare victory with almost 60 percent of the vote.

Tsvangirai, Makoni and Arthur Mutambara, leader of the MDC's smaller faction, told reporters after holding talks that Mugabe had undermined chances of a fair election.

"We believe there is a very well thought out, sophisticated and premeditated plan to steal this election from us," Makoni said after the meeting. "We are satisfied that the integrity and credibility of this election is gravely in doubt."

Mutambara, leader of a group that split from MDC leader Tsvangirai's main faction in 2005, has backed Makoni, who is seen as an underdog behind Mugabe and Tsvangirai.

BATTERED HEALTH SYSTEM

Critics say Mugabe, who turns 84 this month, has maintained a tight grip on power through a combination of ruthless security crackdowns and an elaborate patronage system. Supporters revere him as an independence-era hero who fights for his people.

On national television, Mugabe blamed Zimbabwe's troubles on Western sanctions imposed on him and his allies to try to force reform. Mugabe said the measures had harmed health care in Zimbabwe, one of the countries worst affected by HIV/AIDS.

"Our health sector (once) operated in a regional and international context that was free of the illegal sanctions which weigh us down today," Mugabe said in a ceremony to give 450 cars to senior and middle-level doctors at government hospitals.

Mugabe promised the doctors houses and said he had used his pocket money to buy 300 flat screen televisions for hospitals.

In a procedural move, he told his ministers the cabinet had been dissolved ahead of the election.

"I told them that some would return to government, others will be left behind," Mugabe told a rally in the town of Bindura, 70 km (44 miles) northeast of Harare.

Mugabe has also handed out farm equipment and public buses in what critics say is an attempt to win political favour ahead of the vote in a country where many can no longer afford even basic needs and food and fuel are in short supply.

Nurses and doctors have been on strike to demand more pay and state workers were promised higher salaries by Mugabe in the campaign, but inflation of more than 100,000 percent quickly makes pay rises meaningless.

Critics say Mugabe's policies, particularly seizing white-owned farms to give to landless blacks, have led to ruin.

Saturday's presidential, parliamentary and local council polls are seen as the most important since Zimbabwe's independence from Britain in 1980, but few expect a fair vote.

Mugabe, who must win more than half the presidential vote to avoid a second round run-off that might unite his opponents, rejects accusations of rigging three elections since 2000.

Tsvangirai told a rally in Chitungwiza, just outside Harare, that Mugabe had lost touch with reality.

"So when you vote, don't leave the polling station, we want to see how he will steal," he said. "What Mugabe does not realise is that his system has collapsed."