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JOHANNESBURG, June 10 (Reuters) - Jacob Zuma, leader of South Africa's ruling party, said on Tuesday he was alarmed and anxious about reports of widespread violence and brutality in Zimbabwe's election campaign.

Speaking during a visit to India, Zuma said in a speech released by his African National Congress in Johannesburg: "We cannot rest until the situation is resolved, as it affects all of us. We want to see the return of peace and stability in Zimbabwe as speedily as possible."

U.S.-based Human Rights Watch said on Monday a fair presidential runoff vote in Zimbabwe was impossible as scheduled on June 27 because of a systematic campaign of murder and brutality by the government of President Robert Mugabe.

It said at least 36 people had died in politically-motivated murders and 2,000 were victims of a campaign of killings, abduction, beatings and torture.

Opposition leader Morgan Tsvangirai defeated Mugabe in a March 29 election but fell short of the absolute majority needed for outright victory -- necessitating the runoff later this month.

"We are alarmed and anxious about the reports of violence. If these are accurate, the violence surely puts enormous strain on the preparations for the presidential election run-off that should be held towards the end of this month," Zuma said.

He added that stability was needed to enhance the search for sustainable economic development in southern Africa.

Zuma, front-runner to replace President Thabo Mbeki in elections next year, called on Mugabe's ruling ZANU-PF party to ensure free political activity before the vote.

Mbeki, appointed as a regional mediator last year, failed to end Zimbabwe's crisis and was strongly criticised for his softly softly approach after the March 29 election.

Zuma, who now rivals Mbeki as South Africa's most powerful man, has in contrast been outspoken over Zimbabwe and sharply criticised a five-week delay in issuing the result of the first round of the presidential vote.

In a parallel poll, ZANU-PF lost control of parliament for the first time. (Reporting by Stella Mapenzauswa; Writing by Barry Moody)

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