Image copyright AP Image caption Protests erupted soon after the court ruling on Saturday

At least a dozen people have been arrested in the US city of Cleveland during protests after an officer was cleared of all charges relating to the killing of an unarmed black couple.

Police appealed for calm after unrest continued into Saturday night.

Michael Brelo was cleared of voluntary manslaughter in the 2012 incident, when he fired 15 shots into their car.

A string of high-profile police killings of unarmed black people have sparked civil unrest in the US.

Mr Brelo was one of 13 officers to open fire on Timothy Russell and Malissa Williams during a high-speed car chase. But he was the only one to face charges because he climbed onto the bonnet of their vehicle and fired directly through the windscreen at the pair who were no longer deemed a threat.

Image copyright Reuters Image caption Some 62 police cars were involved in the 22-mile police chase at speeds up to 100 mph

The chase began after police heard what they thought was a gun discharge - but turned out to be the sound of the couple's Chevy Malibu backfiring - as they sped past Cleveland police headquarters.

No gun was found inside the car, and Russell and Williams were each shot more than 20 times.

'No justice, no peace'

On Saturday a judge at the court in Cleveland said that because other officers had fired in a 137-shot barrage, he could not rule beyond reasonable doubt that Mr Brelo was responsible for the deaths.

After the ruling, protesters gathered outside the cordoned-off courthouse, some chanting, "No justice, no peace!"

Dozens more gathered at a recreation ground where a 12-year-old black boy, Tamir Rice, was shot dead after waving a replica firearm last November.

Image copyright Getty Images Image caption Police patrolled the streets in riot gear before and after Saturday's verdict

Image copyright Getty Images Image caption Incidents of use of lethal force by police have sparked race-related protests in recent months

Cleveland police tweeted that they had made "multiple arrests...for unlawful congregation and failure to disperse".

The exact number of arrests was not clear. Deputy police chief Wayne Drummond was quoted by AP as saying 12 people had been arrested, while police spokeswoman Jennifer Ciaccia put the figure above 20.

Three people were arrested after throwing an object through the window of a restaurant and injuring a customer.

Earlier inquiry

Some 200 people also held a mock funeral procession in the city, carrying a black coffin and singing. Some held signs that said: "Will I be next?"

A department of justice inquiry into the deaths of Timothy Russell, 43, and Malissa Williams, 30, concluded several months earlier that Cleveland police had engaged in a pattern of excessive force and violation of civil rights.

County prosecutor Timothy McGinty said he was "profoundly disappointed" with the verdict.

Image copyright AP Image caption Judge O'Donnell said he could not be sure Mr Brelo's shots had killed the pair

Russell's sister, Michele, said Mr Brelo would not "dodge this just because he was acquitted. God will have the final say."

Michael Brelo's lawyer, Patrick D'Angelo, said his client had risked his life during the chase and that the prosecution of the case was "vicious and unprofessional".

Mr Brelo was also cleared of the lesser count of felonious assault.

City and federal officials are investigating police conduct in the case.

There have been serious race-related protests over police use of deadly force in Ferguson, Missouri, and in Baltimore in the past year.

In April, Freddie Gray died in hospital a week after Baltimore police had taken him into custody.

His death sparked weeks of protests and later riots and looting in the city.

In Ferguson, teenager Michael Brown was killed last August by a white police officer. Protests followed, and there was further unrest after a grand jury decided not to charge the officer.