HARARE, Zimbabwe (AP) -- A bomb scare shut down Zimbabwe's Victoria Falls Airport on Friday, forcing the country's president to cancel a planned address at a conference on renewable energy, an official said.

Zimbabwean President Edson Mnangagwa was due to address the conference in the morning, but "had to suspend his trip to allow for investigations which are already underway," presidential spokesman George Charamba said.

Authorities couldn't confirm local media reports that the president's plane made a U-turn while traveling to the conference.

Charamba said that airport authorities were informed by Fastjet airline about an email sent "by a John Doe" claiming a "credible bomb/firearm threat" targeting Zimbabwe's airports.

Security systems are "now on heightened alert," Charamba said, urging people to be calm while investigations proceed.

"While our country is peaceful, and all our ports of entry are well secured, such alerts on possible terrorist attacks are taken very seriously," he said.

The Civil Aviation Authority of Zimbabwe said that the incident had forced some flights to divert or delay landing, and more disruptions were likely "to allow for the continuous monitoring of the environment."

While such incidents are unusual in the southern African country. a 2018 explosion in Zimbabwe's second-largest city, Bulawayo, killed two people and wounded about 50 others during a campaign rally before the presidential election that year.

Mnangagwa, who said the blast occurred just "inches" from him, was unharmed. But two vice presidents and other top officials were among the wounded, and two security aides later died from their injuries. Two men who were arrested after the explosion were later freed for a lack of evidence.