(Changes dateline, recasts with rally)

By MacDonald Dzirutwe

BULAWAYO, Zimbabwe, May 18 (Reuters) - Zimbabwe's main opposition vowed on Sunday to 'bury' President Robert Mugabe at next month's second-round election, and called for the process of checking the poll results to be open to the media.

The Movement for Democratic Change launched its campaign ahead of the June 27 election in the absence of its leader Morgan Tsvangirai, who delayed his return from abroad after the party said it had discovered a plot to kill him.

MDC vice president Thokozani Khupe told about 10,000 supporters in Zimbabwe's second city of Bulawayo that the opposition would win by an even bigger margin after official results from the March 29 first round vote showed Tsvangirai did not secure sufficient votes to avoid a run-off.

The MDC insists Tsvangirai won outright the first time.

"We decided to participate in the run-off to give the people of Zimbabwe a second chance to kick out the dictatorship. We have now declared a zero vote for Robert Mugabe," Khupe told supporters on Sunday.

"We need to give Mugabe a final blow. On June 27 we will be having a ZANU-PF funeral. We are going to make sure we bury them so that they will not resurrect again."

The MDC has alleged electoral fraud in the March election, and Khupe said verification of results in next month's vote should be open to the media and observers and recorded on camera "so that ZANU-PF will not cheat."

Earlier, police set up a security checkpoint on the main road leading to the stadium where the rally was held, stopping and searching vehicles for weapons. At a nearby police camp, four water canons were on standby.

Police had initially banned the rally, but the MDC won a court ruling compelling the authorities not to interfere with the meeting.

"ASSASSINATION ATTEMPT"

Tsvangirai, who left Zimbabwe shortly after the first vote on March 29, had been scheduled to return to home on Saturday to relaunch his campaign, but the party said it had received information about a planned assassination attempt.

"Mr Tsvangirai will not be going to Zimbabwe today. We are still assessing the security situation," his spokesman George Sibotshiwe said from neighbouring South Africa on Sunday.

Next month's second-round election will be held against the backdrop of a political and economic meltdown in which Zimbabweans have grappled with 165,000 percent inflation, 80 percent unemployment, chronic food and fuel shortages which have seen millions flee to neighbouring countries.

The March vote was followed by violence, which the MDC says killed at least 40 of its supporters and which it blames on Mugabe's ZANU-PF party. ZANU-PF in turn accuses the opposition.

Zimbabwe remains in a political stalemate over the presidential poll, although the opposition won enough votes in March to end ZANU-PF's parliamentary majority for the first time since independence from Britain in 1980.

On Sunday state media said the Zimbabwe Electoral Commission (ZEC) would only allow voters registered for the March election in the run-off.

Zimbabwe's government has said Tsvangirai should report security concerns to the authorities, and have sought to cast doubt on talk of an assassination plot. (Additional reporting by Nelson Banya; Writing by Stella Mapenzauswa; Editing by Richard Balmforth) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/)

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