Also on Saturday, Tendai Biti, the secretary general of the MDC, appeared in court in Harare, the capital, on treason charges.
Biti arrived at noon handcuffed. The court was convened to hear the legality of his arrest.
When asked by reporters how he was, Biti said “fine”.
The details of why Biti has been charged with treason have not been made clear by police.
Biti was arrested on Friday on his return from South Africa.
Treason can carry a death penalty in Zimbabwe.
Haru Mutasa, Al Jazeera’s correspondent in Harare, said that Biti has now been ordered to appear in court on Monday to be formally charged.
The arrests have heightened concern that the presidential run-off between Tsvangirai and Mugabe will not be free and fair.
One of two MDC campaign buses was returned on Saturday after being impounded by police the day before.
Violent incidents has broken out across the country since the first round of elections on March 29.
The MDC, which took control of parliament in the first-round vote from Mugabe’s Zanu-PF party, has accused Mugabe of organised intimidation to influence the result of the presidential run-off.
|Tsvangirai has been held on several occasions
in the run-up to the deciding vote [AFP]
The opposition party says that 66 of their members have been killed by Zanu-PF loyalists.
Mugabe says that the MDC has instigated the violence.
Thabo Mbeki, the South African president, has been tasked with mediating between Mugabe and the opposition, but questions have been raised over Mbeki’s credibility.
Vincent Magombe, the director of the research institute Africa Inform International said the South African effort had not been effective in promoting stability in Zimbabwe.
“It has been a total and abject failure, really. It is a shame for South Africans and especially for the president of South Africa that they have been totally unable to give a hand to their neighbouring country,” he said.
“I think the situation was very well articulated by the leaders of neighbouring Botswana, who have come out before anyone else in the region to formally protest against Mugabe’s arrest of opposition leaders [in Zimbabwe].
“[Neighbouring countries] all feel the great pressure of people running away in their millions from Zimbabwe. They know that unless the situation in Zimbabwe is resolved very, very urgently, there will a complete commotion, chaos and instability within the region.”