Zimbabwean police detained opposition leader Morgan Tsvangirai on Friday for the second time this week after blocking him from reaching a campaign rally for the June 27 presidential run-off vote.

The opposition Movement for Democratic Change accuses President Robert Mugabe of trying to sabotage Tsvangirai's campaign in order to preserve his 28-year hold on power.

Tsvangirai was released from the police station at Esigodini, 40 km (25 miles) southeast of Zimbabwe's second largest city Bulawayo, a few hours after being stopped by armed police at a roadblock.

The party called Tsvangirai's detention "a shameless and desperate act".

"The regime must let the president do that which the people of Zimbabwe have mandated him and the MDC, to help restore the dignity of the people of Zimbabwe," it said in a statement.

It said police had banned several planned campaign rallies because authorities could not guarantee the safety of party leaders, adding that it would lodge a High Court action to prevent police interference in the campaign.

Police spokesman Wayne Bvudzijena blamed the opposition for the incident on Friday, saying the MDC convoy crashed through a roadblock.

Tsvangirai, who beat Mugabe in a March 29 election but failed to win the majority needed to avoid a second ballot, was detained on Wednesday and questioned by police for eight hours.

On Thursday, police stopped and held five U.S. and two British diplomats for several hours after they visited victims of political violence. Zimbabwe also barred relief agencies from doing work in the country, suffering economic ruin.

AID BAN

U.S. Ambassador James McGee, among those detained on Thursday, accused the government on Friday of using food aid to try to win votes.

"We are dealing with a desperate regime here which will do anything to stay in power," he told a video conference call from Harare. Washington has blamed the diplomats' detention firmly on Mugabe's government.

The United States and former colonial power Britain say Zimbabwe is trying to intimidate Tsvangirai's supporters. France's foreign ministry also said on Friday it was "extremely worried by the climate of intimidation and violence."

The opposition says 65 people have been killed in violence since the first round of voting. Mugabe blames his opponents.

Mugabe's government suspended the work of all international aid agencies in the southern African nation on Thursday, saying some of them were campaigning for the opposition.

Britain and the European Union demanded the lifting of the ban. U.N. officials said it would increase suffering and CARE, one of the agencies whose work has been suspended, said millions of aid-dependent Zimbabweans were at risk.

EU aid commissioner Louis Michel said: "I am deeply distressed to think that hundreds of thousands of people who depend on aid from the European Commission and others for their very survival now face an even more uncertain future."

Zimbabwe, once one of Africa's most prosperous countries, has seen food production plummet since 2000 when Mugabe's government began seizing thousands of white-owned farms as part of a land redistribution programme to help poor blacks.

Many of the farms have ended up in the hands of Mugabe loyalists, and the country now faces chronic food shortages. It has had to rely on handouts and imports to feed its people.

Mugabe blames sanctions imposed by Western countries for the collapse of the once prosperous economy. The opposition says he ruined Zimbabwe through mismanagement.

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