Zimbabwe's High Court on Sunday ordered police to release an opposition member of parliament who was arrested on Saturday for the second time in a week amid mounting tensions before this month's presidential run-off.

Eric Matinenga was initially arrested on June 1 on charges of inciting public violence in his constituency, but was released on Thursday after a magistrate dropped the charges and said he had been wrongly charged.

He was detained for a second time on Saturday morning.

Matinenga's arrests come amid accusations by the opposition that President Robert Mugabe's government is trying to sabotage Movement for Democratic Change (MDC) leader Morgan Tsvangirai's campaign ahead of a June 27 run-off presidential election.

The second round vote follows a disputed March poll which showed Tsvangirai beat Mugabe, but not by enough votes to avoid a run-off.

"The MDC welcomes the judgement as the only logical thing to do as Advocate Matinenga is a fine son of Zimbabwe, whose quest for the freedom of the people of Zimbabwe is unquestionable," the party said in a statement.

Six MDC lawmakers have been arrested for various offences since the March 29 poll.

Police detained Tsvangirai twice last week as he campaigned in the rural southwestern province of Matebeleland. He was released on Friday a few hours after being stopped by armed police at a roadblock.

On Friday police also banned several of the MDC's planned rallies in the presidential run-off campaign because authorities could not guarantee the safety of party leaders.

The country's High Court overturned the ban on Saturday, allowing the MDC to hold its weekend rallies.

"This apparent harassment by the police is not the only problem we face. Today, ZANU-PF militia and war veterans tried to disrupt two of our rallies in Zengeza and Glen Norah," MDC spokesman Nelson Chamisa told Reuters.

"They came chanting and tried to intimidate our supporters, but the rallies proceeded and they were well attended despite the nuisance. The police did absolutely nothing about the disturbance."

The opposition, rights groups and opposition members accuse veteran leader Mugabe's ruling party of trying to rig the election by intimidating voters, undermining the MDC and thwarting its campaign efforts.

The groups say Mugabe's government has embarked on a violent campaign to intimidate voters as he faces an uphill task of reversing his electoral defeat.

Mugabe blames the MDC for election violence and his government last week ordered all aid agencies to stop their humanitarian programmes, saying they were interfering in the country's politics.

The Southern African Development Community, a regional grouping of 14 nations, including Zimbabwe, is sending observers to monitor the run-off.