On Tuesday it accused the electoral commission of deliberately delaying the results of this week's vote to favour the ruling party, and reported irregularities. Police have been blamed for using live bullets on opposition protesters.
Meanwhile, President Mnangagwa has tweeted that he was "positive" about the results and urged Zimbabweans to patiently wait for the final announcement.
The United States Embassy in Harare is deeply concerned by events unfolding in Harare.
Opposition MDC party supporters burn election posters depicting Zimbabwean President Emmerson Mnangagwa during the protests.
The streets were calm on Thursday morning although many shops were shuttered in the city center.
"I wasn't sure whether it's safe to come to work. Equally, we hold the party and its leadership responsible for any loss of life, injury or damage of property that arise from these acts of political violence which they have aided and abetted", he said.
Elsewhere markets were open and queues formed outside banks - a common sight in Zimbabwe due to the country's chronic shortage of banknotes.
It is a lesson for the opposition that in future they should not lose sight of the bigger prize.
Mnangagwa previously said the opposition was to blame for the violence, though some global observers criticized the military for opening fire on unarmed civilians.
The government has condemned the opposition for the protesters who threw rocks and set fires after the Zimbabwe Electoral Commission said the ruling ZANU-PF party had won a parliamentary majority in the election Monday.
Trump touts economy: 'These numbers are very, very sustainable'
Trade contributed 1.06 percentage points GDP growth in the second quarter after being neutral in the January-March period. That was a pickup from the first quarter's revised growth rate of 2.2 per cent, the New York Times reported .
MDC supporters, who say their leader Nelson Chamisa won the vote, burnt tyres and pulled down street signs as protests spread from the party headquarters in Harare.
From the start it was clear that neither the government nor the opposition would accept defeat in Zimbabwe's election.
Wednesday's violence, which followed a relatively orderly election, dashes President Emmerson Mnangagwa's hopes of repairing the image of a country that had become synonymous with corruption and economic collapse in under Mugabe.
MDC supporters have ripped down a Mnangagwa billboard. "The process must be credible and transparent, then whoever wins this election, Zimbabwe can move on, and the people of Zimbabwe can be the real winners". It called for transparency in the release of results.
Its representative, Angola's Foreign Minister, Manuel Domingos Augusto, called the poll "a political watershed in Zimbabwe's history" that would lead to "consolidation of democracy".
Under Mugabe, elections were often marred by fraud and deadly violence.
At the press briefing, Zec also announced the last of the House of Assembly results, and the MDC Alliance's Elizabeth Java Tsvangirai and Susan Matsunga won the Glen View South and Mufakose constituencies respectively. We have won the popular vote.
ZEC chairwoman Priscilla Chigumba, a high court judge, has flatly denied allegations of bias and rejected accusations of rigging.
His attempts to position Grace as his successor are widely thought to have driven the military to intervene and put their favoured candidate, Mnangagwa, in power.