Several videos of police brutality have emerged during protests over the death of African American George Floyd.
In Buffalo, New York State, two officers were suspended after they were seen shoving an elderly white man to the ground.
And in New York City, police were captured on video roughly handling demonstrators as they ran away.
The reports come hours after a memorial for Floyd in Minneapolis, the city where he died at the hands of police.
His killing, also captured on video, has caused outrage and sparked a wave of protests against racial discrimination and police treatment of African Americans in cities across the US.
The vast majority of demonstrations over the past eight days have been peaceful, but some have descended into violence and rioting, with curfews imposed in a number of cities.
The Buffalo video shows a 75-year-old man approach police officers enforcing a curfew, who then move forward pushing him back, causing him to fall over backwards and hit his head.
As he lies on the ground, blood is seen pouring from his ear.
The man was taken away in an ambulance and was later found to have suffered a severe head injury.
An initial statement from Buffalo Police Department said the man “tripped and fell” during a “skirmish involving protesters”, compounding outrage at the incident on social media.
Police spokesman Jeff Rinaldo later said that the statement came from officers not directly involved in the incident, adding that when the video emerged the two policemen who had pushed the demonstrator had been suspended without pay.
On the same evening, a delivery driver in New York City was arrested 27 minutes after the city’s curfew had started, despite being a key worker exempt from the curfew.
And in the Williamsburg area of the city, police were filmed charging demonstrators, throwing at least one person to the ground.
On Thursday New York State Governor Andrew Cuomo defended police, saying they were not beating citizens “for no reason”, and if they did “it’s wrong”.
City Mayor Bill de Blasio said the authorities were “doing everything from a perspective of restraint”.
But both men have since condemned the incidents which emerged overnight.
“Police officers must enforce – NOT ABUSE – the law,” he said.
Meanwhile Mayor de Blasio said he had complained to the city police department after seeing the video of the arrest of the delivery worker.
The incidents happened as police enforced curfews in dozens of cities across the US after a wave of protests sparked by George Floyd’s death.
Floyd, 46, was stopped by police investigating the purchase of cigarettes with counterfeit money on 25 May in Minneapolis.
A video showed him being arrested and a white police officer continuing to kneel on his neck for several minutes even after he pleaded that he could not breathe.
Protests erupted and have continued since, across many US cities and also internationally, with rallies on Wednesday in Australia, France, the Netherlands and in the UK, where thousands gathered in central London.
Floyd’s death follows the high-profile cases of Michael Brown in Ferguson, Missouri; Eric Garner in New York; and others that have driven the Black Lives Matter movement in recent years.
For many, the outrage over Floyd’s death also reflects years of frustration over socio-economic inequality and discrimination.
Protests over the death continued in dozens of cities on Thursday despite widespread curfews.
They followed a memorial service attended by hundreds, who stood in silence for eight minutes and 46 seconds, the amount of time Floyd was alleged to have been on the ground under the control of police in Minneapolis.
A lawyer for George Floyd told the service that a “pandemic of racism” led to his death.
Giving the eulogy, civil rights activists the Reverend Al Sharpton said it was time to stand up and say “get your knee off our necks”.