Young supporters of Zimbabwe's President Robert Mugabe stoned and beat up backers of Prime Minister Morgan Tsvangirai on Sunday, blocking a planned rally of his Movement for Democratic Change party.
A group of youths singing anthems of Mugabe's ZANU-PF party threw rocks at MDC supporters inside the stadium where the rally was to be held, in the sprawling Harare suburb of Chitungwiza 30 kilometres (19 miles) south-east of the capital, an AFP correspondent said.
Police fired tear gas to disperse the ZANU-PF supporters, but failed to stop them from throwing stones and beating MDC activists, forcing the MDC to cancel the rally before Tsvangirai could deliver his address.
"Unfortunately we are unable to do this rally because of incredible acts of wanton violence, malicious violence that we have suffered at the hands of ZANU-PF this morning," Tendai Biti, MDC secretary general, told a news conference.
Biti said seven MDC activists had to be hospitalised and 15 more treated for injuries, while five party vehicles were damaged.
"There are literally hundreds of people that have been beaten up, that have been stoned by ZANU-PF supporters. They have suffered bruises, tissue injuries, various degrees of injuries", he said.
He said police had failed to protect the MDC.
"They watched us as these ZANU-PF youths destroyed our property and assaulted our members," he said.
Biti, who is also Zimbabwe's finance minister in the power-sharing government between Mugabe and Tsvangirai, accused ZANU-PF of using violence to provoke fear in the run-up to elections expected to be held as soon as next year.
"It is self-evident that ZANU-PF is already building up to the next election. It is quite clear that we are in a chaos scenario where they are unleashing violence," he said.
Police spokesman Oliver Mandipaka said he had received reports of clashes but was still gathering information and could not comment or give details. ZANU-PF national spokesman Rugare Gumbo said he had not heard about the incident.
"But we are not surprised by the claim that ZANU-PF is the one that caused the violence. That is what we always know the MDC will say," he told AFP.
Zimbabwe's unity government has been riven by problems since it was formed in February 2009, after a bitterly disputed first-round 2008 vote where neither candidate won an absolute majority.
That election sparked a wave of attacks that killed more than 200 MDC supporters. To end the bloodshed, Tsvangirai pulled out of the second round against Mugabe, the country's ruler since 1980.
The power-sharing pact was meant to introduce security sector reforms that would prevent a repeat of the violence, but Tsvangirai has accused Mugabe of failing to uphold his end of the deal.
Tsvangirai briefly quit the coalition in late 2009, but regional mediators persuaded him to resume working with Mugabe.
The leaders are supposed to oversee the drafting of a new constitution that will steer the country to fresh elections, but the process has been marred by violent disruptions of community meetings by Mugabe supporters and is running more than a year behind schedule.