Image copyright Reuters

Two police officers who shot and killed a man in Louisiana acted reasonably, the Department of Justice has said.

The death of Alton Sterling outside a grocery shop in Baton Rouge last summer sparked days of protests at a time of heightened race tensions across the US.

In confirming no charges would be brought against the police, the department said Mr Sterling was armed and refused to follow commands.

The Sterling family said they were hopeful the state could bring a case.

Louisiana's attorney general would have a "phenomenal case", the family lawyer said, because the officers' actions were "outrageous, inappropriate and did not follow procedures".

"Alton was human," said Sandra Sterling, Alton's aunt. "He's no longer here but his voice still will be heard, through us. So stay behind Alton. And we don't want this to end. Remember his name."

Video footage of the struggle between the two white officers and the black man triggered days of protests and nearly 200 arrests in Baton Rouge.

Media playback is unsupported on your device Media caption The story behind this photo at Baton Rouge protests

Moments after the family lawyer made his statement, the Department of Justice issued its justification for not bringing charges.

In summary, it said:

the officers' actions were reasonable under the circumstances and lawful

police were responding to a call that someone matching Sterling's description had brandished a weapon and threatened another person

Sterling was large, strong and failing to follow orders

the officers attempted "multiple less-than-lethal techniques" before using lethal force

one of the officers believed Sterling was attempting to use a gun

Whether Mr Sterling was reaching for his .38 caliber revolver is subject to debate because it is not clear from the video, and the Department of Justice could not say either way.

"The evidence simply cannot establish beyond a reasonable doubt the position of Sterling's right hand at the exact time of the shooting," the department said in its statement.

Media playback is unsupported on your device Media caption Pinned down and shot in Louisiana

US Attorney Corey Amundson told a press conference that after a thorough 10-month review, that there was "insufficient evidence" to press charges.

More than 100 people attended a vigil on Tuesday night outside the Triple S Food Mart where Sterling died last July.