Minneapolis Mayor Jacob Frey on Friday declared a strict curfew for the US city after three nights of violent protests over the death of an unarmed African American man in police custody.

Frey ordered everyone off the city’s streets starting at 8 pm (0100 GMT Saturday) until 6 am, excepting law enforcement, fire and medical personnel and national guard troops deployed for peacekeeping.

On Thursday, the protests turned violent as flames ripped through a Minnesota police station and seven protesters were shot in Kentucky as unrest spread across the United States over the deaths of black people during police encounters.

Thousands of protesters gathered in Minnesota, after death of 46-year-old George Floyd who was arrested on on suspicion of using a counterfeit banknote on Monday.

Floyd was unarmed and handcuffed, continously pleaded that he could not breathe. He was soon after declared dead at a nearby hospital on Monday.

The police officer who was involved in the incident arrested on Friday.

Minnesota’s governor Tim Walz earlier called up 500 of the state’s National Guard, but after President Donald Trump tweeted he defended his decision not to put them on the streets as fire gripped the police station.

The Justice Department on Thursday promised to carry out a “robust” investigation into Floyd’s death, saying they will make the case a top priority. Floyd’s family has demanded the officers present when he died face murder charges. All of them have been fired.

On Friday, Trump spoke with the family of Floyd and expressed his grief, saying “I understand the hurt, I understand the pain. People have really been through a lot. The family of George is entitled to justice and the people of Minnesota are entitled to live in safety”.

On Wednesday, demonstrators clashed with law enforcement, looted stores and set fire to shops and a construction site. They were met with police tear gas and rubber bullets.

Earlier, Democratic presidential candidate Joe Biden condemned the incident, saying “We have to ensure that the Floyd family receive the justice they are entitled to”.

The case was seen as the latest example of police brutality against African Americans, which gave rise six years ago to the Black Lives Matter movement.