WASHINGTON — Derek Chauvin, the former Minneapolis policeman convicted of the murder of George Floyd, pleaded not guilty on Thursday in a separate case in which he is accused of striking a Black teenager with a flashlight and kneeling on his neck.

Chauvin, 45, is serving a 22 1/2-year prison sentence for the May 2020 murder of Floyd, a 46-year-old Black man whose death sparked protests against racial injustice and police brutality across the United States.

In the other case, Chauvin is accused of violating the constitutional rights of a 14-year-old Minneapolis boy during a September 2017 arrest.

According to the indictment, Chauvin held the teenager by the throat and struck him multiple times in the head with a flashlight.

He also allegedly held his knee on the neck and the upper back of the boy even after he was lying prone and handcuffed on the ground — a position similar to that which led to Floyd’s death.

Chauvin pleaded not guilty to the charges on Thursday by video from the maximum security Minnesota prison where he is serving his sentence.

Chauvin, who is white, was captured on video kneeling on Floyd’s neck for nearly 10 minutes, until he fell unconscious and died.

Chauvin and three other police officers who were on the scene during Floyd’s fatal arrest pleaded not guilty earlier this week to federal civil rights charges.

They are charged with violating Floyd’s constitutional rights and failing to respond to his medical needs.

A jury took less than 10 hours in April to convict Chauvin of Floyd’s murder at the end of a high-profile trial. The other three police officers are to face state charges next year for their roles in Floyd’s death.