A black man murdered by police - Louisiana rages and protests

There is growing outrage in the US over the killing of an African American man who was pinned to the ground and shot in the chest by two white police officers outside a convenience store in Baton Rouge, Louisiana.

The US Justice Department said on Wednesday it would investigate Tuesday’s killing of Alton Sterling, 37, the latest alleged police brutality against blacks.

A graphic video of the shooting recorded by a bystander shows an officer shooting Sterling five times at close range.

Hundreds of people gathered for a prayer vigil near the spot where Sterling was fatally shot, with activists urging people to protest the "excessive force" used by police against African Americans.

"I'm heartbroken. It's outrageous. It's crazy," said Abdullah Muflahi, the owner of the Triple S Food Mart where Sterling was killed in the parking lot.

Muflahi  said he considered Sterling a friend and allowed him to sell CDs outside his store. He said police took a gun from Sterling's pocket.

Video recorded on the bystander's cell phone shows an officer approaching Sterling and ordering him to lie down. The two officers then tackle him to the ground, with one pulling a gun from his holster and pointing it at his chest.

The officers were responding to a call about a black man reported to have made threats with a gun, according to Baton Rouge Police Chief Carl Dabadie.

Dabadie told a news conference that the two police officers involved, Blane Salamoni and Howie Lake were both put on administrative leave.

Relatives and acquaintances described Sterling as jovial and friendly, a neighborhood fixture who had peddled copied CDs, DVDs and games in front of the Triple S Food Mart for years.

Cameron Sterling, Alton's 15-year-old son, broke down crying at a news conference as his mother spoke. "He was killed unjustly and without regard for the lives he helped raise," said the mother, who did not give her name.

The latest police killing comes as law enforcement departments across the United States face increased scrutiny over allegations of excessive force against black people and other minority groups.

Police in the United States killed over 1,150 people in 2015, with the largest police departments disproportionately killing at least 321 African Americans, according to data compiled by an activist group that runs the Mapping Police Violence project.