The British government says it has summoned Zimbabwe's ambassador to explain the detention of diplomats on Thursday. According to the U.S. embassy, Zimbabwean police detained U.S. and British diplomats, slashing the tires of their cars after they visited victims of political violence ahead of a presidential runoff election. They were released hours later. Correspondent Scott Bobb reports from our Southern Africa Bureau in Johannesburg.

The U.S. Ambassador to Zimbabwe said the diplomats were detained after their vehicles were stopped at a roadblock outside Harare.

Morgan Tsvangirai, leader of Zimbabwe's opposition Movement for Democratic Change, 30 May 2008

The incident came one day after Zimbabwean opposition leader Morgan Tsvangirai was detained for nine hours by police in a similar incident. Tsvangirai is campaigning against President Robert Mugabe in a runoff presidential election due in three weeks.

Tsvangirai's Movement for Democratic Change (MDC) party accused the ruling ZANU-PF party of trying to win the election through a campaign of intimidation. The opposition says more than 60 supporters have been killed and thousands displaced since elections in March in which it won a majority in parliament.

The government accuses the opposition of being behind the violence.

The third runner-up in the presidential vote, Simba Makoni Thursday told delegates at an economic forum in Cape Town that the runoff vote should be cancelled because of the escalating violence. Civic groups have made similar calls.

Kenya's Prime Minister Raila Odinga, told the same forum that although African leaders did not want to appear to be interfering in another country's internal affairs he felt he should speak out.

Kenyan PM Raila Odinga speaks during a session on Kenya at World Economic Forum on Africa in Cape Town, 5 Jun 2008

"I think I would be failing in my duty if I didn't point out that what is happening in Zimbabwe is a big embarrassment to the entire continent of Africa," he said.  "We cannot be speaking of democracy and democratization of the continent when we condone what is happening in Zimbabwe."

Odinga was installed as prime minister after weeks of deadly violence following disputed elections in Kenya, which his party says it won.

Britain, the United States and European Union quickly condemned Tsvangirai's detention. State Department Spokesman Sean McCormack noted that western governments have already imposed targeted sanctions on senior Zimbabwean officials and said hopes for change now lie with Zimbabwe's neighbors.

"States like South Africa, for example, need to use the leverage that they have," he said.  "It is a tragic situation. This is a state that was once a model for southern Africa. It was a net exporter of food, it was a proud state that emerged from a colonial past.  And the rule of one man and his party has really destroyed the economy of the state and really destroyed any tradition of democracy in Zimbabwe."

Thabo Mbeki (file photo)

The South African government says its policy of quiet diplomacy is more effective than public criticism in bringing change in Zimbabwe.  Officials in Pretoria Thursday said the release of Tsvangirai and his entourage came after the personal intervention of President Thabo Mbeki who has been charged by southern African leaders with mediating the Zimbabwean crisis.