He said: "SADC tell me, what you observing, what are you observing?"
"Zimbabwean authorities had a duty to facilitate this in a peaceful manner, without deploying the army to the streets", he said.
Zimbabweans are shocked after the military swept into Harare and opened fire to disperse opposition supporters protesting alleged manipulation in Monday's election.
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"We hold the opposition MDC Alliance and its whole leadership responsible for this disturbance of national peace, which was meant to disrupt the electoral process", Mnangagwa said, according to ZBC.
The United Nations and former colonial power Britain also expressed concern over the violence, and called for "restraint".
Chamisa declared an early victory on Tuesday long before the counting had been completed - including in the rural regions that tend to overwhelmingly support the ruling party.
The streets were calm on Thursday morning although many shops were shuttered in the city center.
In a late-night press conference, Home Affairs Minister Obert Mpofu warned that the government "will not tolerate any of the actions that were witnessed today".
"The opposition. have perhaps interpreted our understanding to be weak, and I think they are testing our resolve and I think they are making a big mistake", he said.
Zimbabwe awaits 1st results of historic, peaceful election
The ZEC boss once again applauded the high vote turnout in the country's first post-Robert Mugabe elections. A run-off vote is scheduled for September 8 if no presidential candidate wins at least 50 percent.
The MDC opposition party condemned the army for opening fire on protesters "for no apparent reason".
Tendai Biti, a candidate for opposition party Movement for Democratic Change (MDC), has accused the ruling Zanu-PF regime of plotting to assassinate himself and Chamisa.
President Emmerson Mnangagwa of Zimbabwe said on Thursday he has been talking to opposition leader Nelson Chamisa to try to defuse tension over the Monday presidential election after violent clashes on the streets of Harare.
The riots surged up to the fence of the Rainbow Towers Hotel & and Conference Centre, where the electoral commission has been announcing results and many global election observers are staying.
ZEC said the final results of the presidential race may not be known until Saturday.
In Harare, the contrast could not be starker with November, when hundreds of thousands filled the streets, hugging soldiers and celebrating their role in ousting 94-year-old Mugabe, the only leader Zimbabwe had known since independence in 1980.
Traditional community chiefs have traditionally been close to the ZANU-PF, though a growing number have been at loggerheads with Mnangagwa's government.
A credible vote is crucial to the lifting of worldwide sanctions imposed on Zimbabwe so that its collapsed economy can recover. Final results must be released by August 4.
The observers had been invited by the ZANU-PF's leader, President Emmerson Mnangagwa as part of his "guarantee" of a "free, fair and transparent election" and their verdict on the poll was mixed.
But the dispute over the conduct of the elections and the subsequent violence has punctured the euphoria over the army's removal of longtime strongman Robert Mugabe last November and the hope that Zimbabwe might be entering a new era of democracy after decades of political repression and economic ruin.