US President Donald Trump has called for the investigation into the death of Minnesota man George Floyd to be expedited following global outrage, declaring "justice will be served".
Floyd, an African-American man, died on Monday (local time) after a white police officer knelt into his neck for eight minutes while placing him under arrest for a suspected forgery.
Video of the incident taken by a bystander led to headline news across the world and protests in the US.
The footage shows Floyd gasping for air and groaning "I can't breathe" while distressed bystanders ask the officer to let him up.
Now Trump has announced on social media the FBI and US Department of Justice are already "well into" an investigation of the death.
"I have asked for this investigation to be expedited and greatly appreciate all the work done by local law enforcement," he posted.
"My heart goes out to George's family and friends. Justice will be served!"
Four officers involved in the fatal apprehension of Floyd were dismissed from the police force on Tuesday (local time).
Minneapolis mayor Jacob Frey has also called on prosecutors to file criminal charges against the officers involved.
"Why is the man who killed George Floyd not in jail? If you had done it or I had done it we would be behind bars right now," Frey said during a news briefing.
"I am calling on Hennepin County Attorney Mike Freeman... to charge the arresting officer in this case."
The Police Officers Federation of Minneapolis, the union that represents the city's police force, said in a statement to local media the officers were cooperating with the investigation and it was "not the time to rush to judgment".
"We must review all video. We must wait for the medical examiner's report," the union said, asking the community to remain calm.
Frey did not specify what charge he thought was appropriate for the officer, but said he has relayed his wish to the prosecutor in the county where Minneapolis is located.