* Tensions high in strike-hit mining region
* ANC expected to retain power in May 7 poll (Adds police confirmation and background)
By Ed Stoddard
JOHANNESBURG, April 27 (Reuters) - Police used water cannon and stun grenades to disperse rioters in South Africa's strike-hit platinum belt on Sunday after a government minister was attacked by rock-throwing protesters while campaigning for the May 7 election.
Police spokesman Thulani Ngubane told Reuters a community hall, municipal centre and the house of a councillor for the ruling ANC were burnt down. He would not identify the rioters but local media and union leaders said the minister had been attacked by members of the striking AMCU miners' union.
Ngubane confirmed sports minister Fikile Mbalula had to be whisked away under police protection after he and the ANC activists he was campaigning with were confronted by a crowd in the shanty town of Freedom Park northwest of Johannesburg.
It was after this that the protest erupted into a full-scale riot, Ngubane said.
Sydwell Dokolwana, the regional secretary for the National Union of Mineworkers (NUM), a key ANC ally and AMCU's arch rival, told Reuters he was with the minister at the time and that several people were hurt in the scuffle.
"There was a group of about 100 guys with AMCU shirts. We had to run for our lives," he told Reuters.
"They said they would only allow us to campaign if the ANC assisted them in getting 12,500 rand ($1,200)," he said.
AMCU's battle cry has become "12,500 rand", which is the minimum monthly wage it is seeking from the world's top platinum producers, Anglo American Platinum, Impala Platinum and Lonmin.
While it has backed down from an initial demand that this wage, over double current levels, be granted immediately, its 70,000 members remain off the job after wage talks last week aimed at ending the 13-week-old strike collapsed.
Employers have taken their latest offer directly to the workers, betting that AMCU's rank and file have lost their will to strike after going three months without pay.
AMCU officials could not be immediately reached for comment on the outbreak of violence.
The AMCU/NUM rivalry adds fuel to an already combustible social and political mix in the area, which has been hard hit by the strike.
Households and local businesses are struggling as the miners have collectively lost almost 7 billion rand ($660 million) in wages, according to an industry website that constantly updates the tally. (http://www.platinumwagenegotiations.co.za/)
AMCU emerged as the top union in the platinum shafts after poaching tens of thousands of NUM members in a vicious turf war in 2012 that killed dozens of people and triggered a wave of violent wildcat strikes that year.
South Africa on Sunday marked two decades of multi-racial democracy, 10 days before elections which are expected to keep the ANC in power.
The flare-up on the platinum belt reflects the huge tensions in the "rainbow nation", which has glaring income disparities and often violent labour unrest.
($1 = 10.6410 South African Rand) (Editing by Andrew Roche)