Bulawayo, Zimbabwe(CNN) Zimbabwe's government is calling an explosion Saturday an assassination attempt on President Emmerson Mnangagwa, who was holding a campaign rally at a stadium.

Zimbabwean President Emmerson Mnangagwa at Saturday's rally.

The President escaped injuries, but others were injured and hospitalized. A security officer had to have a leg amputated, presidential spokesman George Charamba said. The blast occurred at White City Stadium in Bulawayo.

Forty-nine people were injured, Charamba said.

"This incident doesn't stand in the way of (the) electoral program," he said. "It doesn't undermine the security of the country, but we are jolted. We are not used to this kind of violence."

A "complex investigation" is underway, he said.

"The President's response has been: We answer with love. We must not speculate ahead of investigations," Charamba said.

The country's two vice presidents were among the injured, the state-run newspaper The Herald reported. Kembo Mohadi suffered leg injuries, and Constantino Chiwenga had slight facial bruises, state media said.

Chiwenga's wife was also hospitalized, but she has been treated and released, Charamba said.

Injured people receive help after Saturday's blast in Bulawayo. CNN has blurred the faces of the injured.

Other injured officials include Oppah Muchinguri-Kashiri, minister of water, environment and climate, and Engelbert Rugeje, party secretary of the ruling ZANU-PF.

Mohadi remained hospitalized early Sunday, as did Muchinguri, Charamba said.

The Zimbabwe Broadcasting Corp. said three of its crew members were hurt and taken to Mpilo Hospital in Bulawayo

The US Embassy in Harare condemned the attack.

"Political violence in any form is unacceptable & contrary (to the) positive progress required (to) move Zim forward as it seeks (to) take its place on the global stage," the embassy said on Twitter. "Our thoughts & prayers go out (to the) victims & their families."

Nelson Chamisa, an opposition leader in Zimbabwe, denounced the stadium explosion. Chamisa heads the Movement for Democratic Change and is a contender for president in elections next month.

"Our prayers go out to the injured and we hope no lives have be lost," Chamisa said. "Violence must have no place in our politics. May God bless and protect the country we all love."

The presidential elections will be the first since the country's military forced Robert Mugabe out of office in an apparent coup in November.