A black therapist in the US state of Florida trying to calm a man with autism in the middle of the street says he was shot by police, even though he had his hands in the air and repeatedly told them that both were unarmed.

The moments before the shooting on Monday were recorded on cellphone video, showing Charles Kinsey lying on the ground with his arms raised, talking to his patient and police throughout the standoff with officers, who appeared to have them surrounded.

"As long as I've got my hands up, they're not going to shoot me. This is what I'm thinking. They're not going to shoot me," he told WSVN-TV later from his hospital bed, where he was recovering from a gunshot wound to his leg.

"Wow, was I wrong."

The shooting comes at a time of growing tensions and increased protests against the disproportionate number of African Americans killed by the police. 

North Miami Police Chief Gary Eugene said on Thursday he had asked Florida state officials to lead the investigation into the shooting.

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Eugene said officers responded to a 911 emergency call about an armed man threatening suicide, but the chief told reporters no gun was recovered at the scene.

Kinsey said he was trying to calm his 23-year-old patient who had run away from the group home where he works. 

"All he has is a toy truck in his hand," Kinsey can be heard saying in the video, speaking of his patient, who was holding a toy. "That's all it is. There is no need for guns."

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Al Jazeera's Andy Gallacher, reporting from North Miami, said: "The video at that point goes black, but we are told that a police officer fired three rounds towards Kinsey, one of them striking him in his leg.

Gallacher said the incident came "at a very sensitive time" in the US.

"We had recently two officer-involved shootings of African American men, and eight officers targeted by other gunmen who allegedly were going after them in response to those shootings."

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Baton Rouge, in the US state of Louisiana, recently became the scene of large protests against police brutality after officers shot dead 37-year-old Alton Sterling on July 5 outside a supermarket, claiming he had a gun.

The father of five had been selling CDs.

Footage of the moment Sterling was killed was also captured on a mobile phone and circulated online, sparking outrage and then protests.

Sterling's killing was followed the next day with another police shooting. An officer killed a 32-year-old black man, Philando Castile, at a traffic stop in the midwestern US state of Minnesota. The aftermath of the shooting was also captured on video and streamed live by Castile's girlfriend on Facebook.

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The deaths sparked outrage and protests in many cities across the US.

Just days later, five white police officers were shot dead at one such protest in Dallas, Texas.

Police identified Micah Xavier Johnson, 25, as the suspect and said he had set out to kill white people. Police shot and killed Johnson after the incident.

The Black Lives Matter movement - which campaigns against police killings of African Americans - disavowed the killing of the officers and said in a statement it stands for "dignity, justice and respect".

The Guardian has documented at least 598 people killed by police across the US so far this year. From that total, 148 - nearly 25 percent - were Black, although African Americans constitute only around 13 percent of the country's total population.

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Source: Al Jazeera and agencies