The governor of the US state of Minnesota summoned the National Guard to help restore security, after two days of violent protests in the city of Minneapolis over the death of a black man seen in a video recording as he struggled to catch his breath, while a white police officer crouched his knee above his neck.

Governor Tim Walls has commanded the National Guard to assist the police, while local and federal officials are seeking to ease the racial tensions sparked by the arrest of George Floyd, 46, on Monday evening, leading to his death.

The four policemen who took part in the incident, including the officer who was seen pressuring his knee, were fired on Floyd's neck, which was lying on the ground.

In a morning press briefing, the police chief, Madaria Madrondo, apologized to the Floyd family, saying, "I am deeply sorry for the pain, destruction and shock that the death of Mr. Floyd has left in the hearts of his family, his family and our community."

Hours later, during a joint press conference, officials overseeing investigations from the Justice Department, the FBI, the Criminal Investigation Office, and the local prosecution called for calm while they were gathering evidence.

"Give us time to get the job done appropriately, and we'll do the justice for you, I promise you," Mine County Prosecutor Mike Freeman told reporters. He admitted that the policeman's style shown in the video was "appalling" and said, "My job is to prove that he violated a criminal law."

Protesters set fire to and damaged some property in Minneapolis (Reuters)

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On Wednesday evening, disturbances occurred for the second consecutive night, and looting and spirits spread, which started hours after Mayor Jacob Frye urged the local prosecutors to bring criminal charges in the case.

In the same vein, the US House of Representatives Judicial Committee asked the Justice Department to investigate systematic misconduct by the police, following the death of a number of African Americans at its hands.

The death of George Floyd in Minneapolis, as well as Brianna Taylor, who was shot in her apartment in Louisville, Kentucky, raises questions about whether the police are involved in "a pattern or practice of conduct contrary to the constitution," as Speaker of the House Judicial Committee Gerold Nadler and other Democrats wrote. To Justice Secretary William Barr in a letter.

The letter also requests the administration to investigate local law enforcement authorities who were responsible for investigating the death of Ahmed Arberry, another unarmed black man who was shot dead by a former police officer and his son while he was running in his neighborhood in Georgia.

"Public confidence in the administration of justice has become a real test ground for the deaths of African Americans," Nadler wrote.