HARARE, Zimbabwe — Presidential election results showing that the man who ousted Robert Mugabe in a coup last year in Zimbabwe had won his own term in office were “fraudulent and illegitimate,” the main opposition candidate said on Friday as he vowed to challenge them in the courts.
Tension seemed to build just hours after election officials said President Emmerson Mnangagwa, who seized power last fall with the military’s backing, had defeated his main rival, Nelson Chamisa, in Monday’s voting.
Police officers tried to break up Mr. Chamisa’s news conference before it began, entering the Bronte Hotel in the capital, Harare, and ordering a large crowd of journalists to leave. But the government’s information minister, Simon Khaya-Moyo, directed the police to stand down and allow the news conference to proceed.
The same sort of tense calm prevailed throughout Harare on Friday, with some businesses closed after violent unrest earlier in the week. At least six people died in clashes between the police and opposition supporters who claimed that the election had been rigged.
A coalition of independent groups that were observing the election said the official results — showing Mr. Mnangagwa with 50.8 percent of the vote, and Mr. Chamisa with 44.3 percent — were consistent with its own estimates, despite irregularities at some polling places.
Turnout was almost 85 percent after a generally peaceful campaign, the first since Mr. Mugabe was ousted last November after 37 years in power.
At his own news conference, Mr. Mnangagwa said that he had won the election fairly, and that he would establish an independent commission to investigate the violence that followed. He also appeared to extend an olive branch to the opposition, saying he would be a president for the entire country, “for those who voted for me and for those who did not.”
“To Nelson Chamisa, I want to say you have a crucial role to play in Zimbabwe’s present and in its unfolding future,” he said.
Mr. Chamisa, 40, called on his supporters to refrain from violence, but he had harsh words about the conduct of the election and he declared a day of “mourning over democracy.” The police, he also said, had raided his campaign office in search of his party’s poll-monitoring reports, which he claimed showed the true results.
Mr. Mnangagwa, 75, the leader of the governing ZANU-PF party, is a former chief of state security and intelligence services. As Mr. Mugabe’s chief enforcer, he was seen as playing a leading role in vote-rigging in past elections.
But hoping to attract renewed investment from the West, Mr. Mnangagwa worked during the campaign to moderate his image with a message that Zimbabwe was embracing democracy and human rights. Critics have seen his election as little more than an extension of Mr. Mugabe’s long rule.
Mr. Chamisa said the violent response by the government to protests this week, with officers firing live ammunition, showed that it feared majority rule. “This cannot be a behavior of people who have won,” he said. “It can only be a behavior of those who have lost.”
On Friday, Mr. Mnangagwa said he did not approve of the actions of the police officers who tried to break up Mr. Chamisa’s news conference. On Twitter, he wrote that such scenes “have no place in our society and we are urgently investigating the matter to understand exactly what happened.”
Earlier this week, the Electoral Commission said that ZANU-PF had won more than two-thirds of the seats in Parliament.