Media playback is unsupported on your device Media caption The BBC's Aleem Maqbool reports on biggest protest so far

More than 1,000 protesters have marched in Baltimore over the death of a black man in police custody a week ago.

But after hours of peaceful demonstrations, some protesters smashed police windows and shop fronts. At least 12 people were arrested.

Freddie Gray was arrested by police on 12 April and then suffered spinal injuries leading to death a week later.

His twin sister, Fredricka Gray, appealed for calm, saying her family wanted the violence to stop.

As clashes began on Saturday evening, she said: "Freddie Gray would not want this."

The Baltimore Mayor, Stephanie Rawlings-Blake, speaking alongside Ms Gray, said she was "profoundly disappointed" by the unrest, blaming it on "agitators".

Image copyright Reuters Image caption Protests were for the most part peaceful

Image copyright Reuters Image caption But they later turned violent, with more than a dozen arrests made

Six police officers have been suspended following the death and an internal police investigation is under way.

Gray, who was 25, is the latest of a series of black Americans to die in police custody in recent months, triggering angry protests accusing the police of brutality.

Baltimore has seen daily protests since his death on Sunday but Saturday's was expected to be the largest so far.

One of Saturday's rallies, organised by the People's Power Assembly, made its way from the Sandtown neighbourhood where Gray was arrested to the Western District police station where an ambulance was called for Gray once he arrived in a police van, injured.

Another rally, called by Black Lawyers for Justice and other groups, congregated outside City Hall.

"Things will change on Saturday, and the struggle will be amplified," Malik Shabazz of Black Lawyers for Justice told WBAL-TV Baltimore. before the march began. "It cannot be business as usual with that man's spine broken, with his back broken, with no justice on the scene."

Image copyright AFP Image caption Protesters held a "die-in", lying in the street to block traffic

Image copyright Getty Images Image caption The case is one of several involving black US men dying in police custody

However, in the evening some demonstrators started to smash shop windows and there were some fights with baseball fans before the game between the Baltimore Orioles and the Boston Red Sox.

Police Commissioner Anthony Batts admitted at a news conference on Friday that officers repeatedly failed to give Gray the medical attention he was due and that, contrary to policy, Gray was not strapped into his seat in the police van following his arrest.

The police will report the findings of their investigation on 1 May, when protesters hope the six suspended police officers will be charged - and have vowed further protests if they are not.

An independent review by state prosecutors will follow.

But the police officers' union has criticised Commissioner Batts' comments about failures in the treatment of Freddie Gray, saying they were "politically driven" and premature.