(Adds comments by S.Africa's ANC President Jacob Zuma)

By Cris Chinaka

HARARE, May 20 (Reuters) - Zimbabwe's opposition on Tuesday accused the government of President Robert Mugabe of setting up a sham investigation into election violence to deflect international attention from brutality by its supporters.

The Movement for Democratic Change opposition says 43 of its members have been killed and scores forced out of their homes by militias loyal to Mugabe since disputed March elections.

It says the violence is intended to help rig a June 27 run-off presidential vote pitting Mugabe against MDC leader Morgan Tsvangirai.

MDC spokesman Nelson Chamisa said on Tuesday the party was prepared to participate in joint committees set up by Mugabe's ZANU-PF to clamp down on electoral violence.

But he said the ruling party was merely on a damage-control exercise.

"ZANU-PF made those overtures to us because they are now under very serious pressure from the international community to stop the violence they are waging against our structures, but I don't think they have any intention to stop," he told Reuters.

Last week, Justice Minister Patrick Chinamasa proposed the joint committees to tackle violence, but Chamisa said the aggression against opposition members had continued unabated.

"The violence has not stopped and MDC supporters are still being brutalised and being forced out of their constituencies as part of the grand plan to rig the elections," he said.

RECOVERY PROCESS

According to official results, which did not emerge for five weeks after the March 29 election, Tsvangirai beat Mugabe but fell short of the absolute majority needed for outright victory.

Jacob Zuma, leader of South Africa's ruling African National Congress, said in an interview with the BBC World Service the elections were discredited due to the long delay in releasing the results.

"It is unacceptable that the electoral commission should hold results ... we are criticising the electoral commission. Those elections are discredited -- that is our view, from the ANC point of view."

Zimbabweans hope the run-off will start recovery from an economic collapse that has brought 165,000 percent inflation, 80 percent unemployment, chronic food and fuel shortages and has sent millions fleeing to nearby countries.

The MDC vows to "bury" Mugabe in the run-off, ending his uninterrupted rule since independence from Britain in 1980.

ZANU-PF denies it plans to rig the polls but has vowed that Mugabe will win the run-off because it could not afford to lose power to an opposition backed by "white imperialists".

The state-owned Herald newspaper on Tuesday quoted ZANU-PF spokesman Nathan Shamuyarira as dismissing MDC charges that state security agents planned to assassinate Tsvangirai.

"The allegations by the Tsvangirai-led MDC have no foundation whatsoever except in his own dreams. No-one in ZANU-PF or government has any intention of killing him," he said.

The MDC said the plot forced Tsvangirai to postpone his return to the country last weekend.

Mugabe's ZANU-PF lost control of parliament on March 29 for the first time since the 84-year-old ruler took power. (Writing by Marius Bosch; Editing by Barry Moody)