Image copyright Reuters Image caption Police use of force against African Americans has been an ongoing issue in the US

Protests by the Black Lives Matter group have taken place in the US states of Minnesota and California on one of the busiest retail days of the year.

The demonstrators in Minnesota temporarily closed the international airport and interrupted Christmas shopping at the Mall of America.

Police said a total of 15 people were arrested at both places, mostly for trespassing or obstructing justice.

Protesters are angry over a police shooting of a black man in Minneapolis.

Jamar Clark was shot dead last month by officers responding to an assault complaint, in one of a number of recent incidents around the US. Activists say he was shot in the head while handcuffed.

Image copyright Getty Images Image caption Police were deployed in force at the Minneapolis-St Paul International airport

Image copyright Reuters Image caption The protests meant that travellers heading to the airport faced lengthy delays

There have been daily demonstrations in Minneapolis over Mr Clark's killing.

Hundreds of people took part in the protest at the mall, one of the largest in North America, where Black Lives Matter organisers promised to congregate in defiance of a judge's warning that the shopping centre's owners could legally block the demonstration.

Police said it was an "unauthorised demonstration" and at one point described the situation as "very, very dangerous".

Image copyright Reuters Image caption Black Lives Matter protesters silently walked out of the Mall of America after staging their protest

Police and mall security staff were speedily deployed against the protesters, warning that any who did not depart immediately would be arrested. For a while the area surrounding the mall was on lockdown, but most stores were only closed for about an hour.

The San Francisco Chronicle separately reported that eight protesters blocking southbound traffic on the 405 freeway near the California city's international airport were arrested on Wednesday.

Pictures of the demonstrators on social media showed them holding a sign demanding justice for Mario Woods, a black man shot dead by police who is suspected of a San Francisco stabbing.

Black Lives Matter is a loosely organised movement which was formed following protests over police killings of black men in Ferguson, Missouri, New York and other cities.

Police use of force against African Americans has been an ongoing issue.

Protests have been held nationwide for more than a year after a series of incidents, some of them fatal.