Zimbabwe's president was unscathed on Saturday by an explosion at a campaign rally that state media called an attempt to assassinate him, later visiting his two injured vice presidents and declaring the "cowardly act" will not disrupt next month's historic elections.Dramatic footage showed a smiling President Emmerson Mnangagwa walking off the stage and into a crowded tent where the blast occurred seconds later, sending up smoke as people screamed and ran for cover. Officials said Mnangagwa was whisked from the stadium rally to a nearby government building in Bulawayo, a traditional opposition stronghold.The explosion went off a "few inches away from me, but it is not my time," the president told state broadcaster ZBC. Mnangagwa, who has joked openly about multiple attempts on his life in the past, said he was used to them by now.At least eight people were injured, the state-run Herald newspaper reported. Vice President Kembo Mohadi had leg injuries, while Constantino Chiwenga, a second vice president and the former military commander, had bruises on his face, the report said. Most of the injured were discharged from a hospital after treatment, presidential spokesperson George Charamba told the newspaper.New uncertainty The blast and the lack of clarity about who was behind it injected new uncertainty into preparations for the July 30 elections, the first since longtime leader Robert Mugabe stepped down in November after a military takeover. Mnangagwa, who had been fired as Mugabe's deputy in a ruling party feud shortly before the power transition, took over with pledges to deliver free and fair elections.Mnangagwa said on Twitter that he was awaiting further information about the blast but added, without elaborating, that those responsible must have come from "outside Bulawayo." He added: "I can assure you these are my normal enemies."He had fled Zimbabwe shortly after his firing in November by Mugabe, who along with his wife, Grace, had sharply criticised the man who had been his closest confidant for many years.Mnangagwa on Saturday evening appealed to the southern African nation for unity."The campaign has been conducted in a free and peaceful environment, and we will not allow this cowardly act to get in our way as we move towards elections," he said.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and FacebookZimbabwe's main opposition leader, Nelson Chamisa, said on Twitter: "Our prayers go out to the injured and we hope no lives have been lost. Violence must have no place in our politics. "The United States and Britain were among countries that condemned the explosion. The US Embassy said on Twitter that "political violence in any form is unacceptable" and contrary to the progress needed to move Zimbabwe forward and "take its place on the global stage".The blast came just hours after a similar attack in Ethiopia, where a grenade explosion killed at least one person and injured scores just after the new, reformist prime minister addressed a huge rally in the capital.Zimbabwe's election next month will be the first without Mugabe since independence from white minority rule in 1980. Mnangagwa, a former justice and defense minister who served for decades as Mugabe's enforcer, has invited Western election observers for the first time in almost two decades.Past votes have been marked by violence and fraud, and the United States and others have said a credible vote is key to lifting international sanctions.