“Brutal killing of #GeorgeFloyd by Minneapolis' white man in uniform in cold blood is a harrowing demonstration of systematic racism and white supremacism glorified by the current administration,” Mousavi wrote on his Twitter account on Thursday with the hasghtag #American_human_rights.
A video has surfaced showing brutal treatment of an unarmed black man under the knee of a US police officer before his death.
George Floyd died after being pinned down by a white officer despite yelling: "I cannot breathe."
Police-involved shootings and killings of unarmed black men in the hands of white police officers in the US have led to mass protests across the country in recent years and the formation of the Black Lives Matter movement.
US police killed nearly 200 people in the first four months of 2020, according to reports.