"We wonder from whom Mr Tsvangirai is running away or hiding," Chihuri said. The MDC leader said earlier this year there was a plot by the Mugabe government to kill him.
Announcing his withdrawal from the election on Sunday, Tsvangirai said his supporters would have risked their lives by voting, and said he was ready to negotiate with Mugabe's ZANU-PF party if the violence stopped.
Concern mounted both within and outside Africa over Zimbabwe's political and economic crisis, which has flooded neighbouring states with millions of refugees. Both the African Union and Southern African Development Community (SADC) were discussing the situation following Tsvangirai's pullout.
Former colonial power Britain said Mugabe must be declared an illegitimate leader and sanctions should be stiffened against his inner circle, which Prime Minister Gordon Brown called "a criminal and discredited cabal".
U.S. Secretary of State Condoleezza Rice said even if the run-off went ahead it would not legitimise Mugabe's government.
Several countries have urged a unity government to end Zimbabwe's dire crisis but both sides have previously rejected this. Analysts said Tsvangirai's withdrawal was likely to delay any solution of this kind.
Mugabe, 84, who has been in power since independence in 1980, has vowed never to hand over to the opposition, branding them puppets of the West.
He denies his supporters are responsible for the violence, which broke out after he and ZANU-PF lost elections on March 29. Official figures showed Tsvangirai fell short of an absolute majority in the presidential vote, forcing the run-off.
Mugabe has presided over a slide into economic chaos, including 80 percent unemployment and the world's highest inflation rate of at least 165,000 percent.
The African Union's top diplomat said he was consulting AU Chairman and Tanzanian President Jakaya Kikwete, the SADC and South African President Thabo Mbeki - the region's designated mediator on Zimbabwe - to see what could be done.
Jean Ping said the withdrawal and the political violence were "a matter of grave concern to the Commission of the AU".
SADC foreign ministers were discussing the Zimbabwe crisis in Luanda. Angolan Foreign Minister Joao Bernardo de Miranda was quoted by the state-run news agency ANGOP as saying the situation was extremely serious and Friday's vote would not be free and fair.
The Dutch government, a major aid donor to Zimbabwe, called on the United Nations, the European Union, the AU and neighbouring states to discuss new steps against Mugabe.
