President Emmerson Mnangagwa urged Zimbabweans to unite on Friday after he was declared the first elected head of state since Robert Mugabe's removal from power, but the opposition leader insisted he had won and pledged to challenge the result.

Sounding a conciliatory note after six people were killed in a post-election crackdown by the military, Mnangagwa vowed to be president for all Zimbabweans and declared that rival Nelson Chamisa would have a vital role to perform in Zimbabwe's future.

He also said the army's use of violence in Harare after the vote would be investigated independently, although he also suggested he understood the resort to military force, remarking that police had been overwhelmed by opposition demonstrators.