Zimbabwe opposition leader Nelson Chamisa declared "a day of mourning for democracy" following his election defeat to President Emmerson Mnangagwa.
Mr Chamisa, leader of the MDC Alliance, said he rejected the result during a press conference, which riot police attempted to break up by trying to disperse journalists while they were awaiting the statement at a Harare hotel.
Apologies to international journalists for the behaviour of Zimbabwe were made, as Mr Chamisa explained how MDC officers were raided for reasons unknown, while members of the party were persecuted and intimidated during the campaign.
Police try to break up press conference
"Today is a day of mourning over democracy," Mr Chamisa said.
"We do not believe in violence, we do not believe in anarchy, we do not believe in weapons of war.
"The thank you we are getting for being law abiding is the thank you of bullets."
The MDC Alliance have evidence of vote-rigging, according to Mr Chamisa, who then claimed that authorities were unwilling to listen to them.
"Mr Mnangagwa did not win this election. This country was won by the MDC presidential candidate, he said. "Fraudulent, illegal, illegitimate, and characterised by credibility gaps."
Zimbabwe’s President Mnangagwa won Monday’s election as the ruling party maintained control of the government in the first vote since the fall of longtime leader Robert Mugabe.
The opposition is almost certain to challenge the results in the courts or in the streets.
Mr Mnangagwa received 50.8% of the vote while main opposition challenger Nelson Chamisa received 44.3%.
Zanu-PF supporters celebrate President Mnangagwa's win
While election day was peaceful, in a break from the past, deadly violence on Wednesday against people protesting alleged vote-rigging reminded many Zimbabweans of the decades of military-backed repression under Mr Mugabe.
Western election observers who were banned in previous votes have expressed concern at the military’s “excessive” force in the capital, Harare.
Their assessments of the election are crucial to the lifting of international sanctions on a country whose economy collapsed years ago.
Following the tension and violence, ITV News Africa Correspondent John Ray has said that the US and EU are yet to endorse President Mnangagwa's disputed victory.
Shortly before the election commission’s announcement, a man who said he was the chief agent with Mr Chamisa’s opposition alliance claimed that they had not signed the election results and rejected them.
Police asked him to step aside.
Commission chair Priscilla Chigumba urged the country to “move on” with the hopeful spirit of election day and beyond the “blemishes” of Wednesday’s chaos, saying: “May God bless this nation and its people.”
Earlier on Thursday, the ruling party and the main opposition group both claimed victory, deepening a political crisis that was worsened by Wednesday’s violence in Harare as the military swept in with gunfire to disperse opposition supporters alleging vote-rigging.
Zimbabwe's capital Harare has been unusually quiet in the hours after President Mnangagwa was declared victorious, with deserted roads appearing to be free from the troops had been circulating.
Water cannons and police remain present, however, at the headquarters of the main opposition party, a day after authorities raided it.
The death toll has risen to six, with 14 injured, police said.
18 people were arrested at the offices of the main opposition party after a vote that was supposed to restore trust in Zimbabwe after decades of Mr Mugabe’s rule.
While Mr Mnangagwa and the ruling party accused the opposition of inciting the violence, the opposition, human rights activists and international election observers condemned the “excessive” force used against protesters and appealed to all sides to exercise restraint.
The international election observers also urged the commission to reveal the presidential results as soon as possible, saying delays would increase speculation about vote-rigging.
Mr Mnangagwa called for an “independent investigation” into Wednesday’s violence, saying those responsible “should be identified and brought to justice”.
Incumbent President Mnangagwa was a longtime Mugabe confidante before his firing in November led his allies in the military to step in and push Mr Mugabe to resign after 37 years in power.
Thousands of jubilant Zimbabweans celebrated in the streets of Harare, greeting the military with selfies and cheers.
Since taking office, the 75-year-old Mr Mnangagwa has tried to recast himself as a voice of reform, declaring that Zimbabwe was “open for business” and inviting long-banned Western election observers to observe Monday’s vote, which he pledged would be free and fair.