Citizens went to the polls on Wednesday but voting had to be extended into Thursday in some areas, including the capital, Harare, due to a lack of ballot papers.
President Emmerson Mnangagwa secured a second five-year term in results announced late on Saturday.
His party, ZANU-PF, has been in power since 1980, following the end of white minority rule in the southern African country, formerly known as Rhodesia.
Mr. Mnangagwa, 80, received more than 52 per cent of the vote, according to media reports. Opposition candidate Nelson Chamisa, 45, received 44 per cent. His party, Citizens Coalition for Change, rejected the results.
The UN chief was concerned about the arrest of electoral observers, reports of voter intimidation, threats of violence, harassment and coercion.
“The Secretary-General calls on political leaders and their supporters to reject any and all forms of violence, threats of violence, or incitement to violence, and to ensure that human rights and the rule of law are fully respected,” the statement said.
“The Secretary-General calls on political actors to peacefully settle any disputes through established legal and institutional channels, and urges the competent authorities to resolve any disputes in a fair, expeditious, and transparent manner to ensure that the results are a true reflection of the will of the people.”