Philando Castile was shot in his car in St Paul, Minnesota, on Wednesday as he reached for his driving licence, his girlfriend said in a Facebook Live video taken during the aftermath.
His death follows that of Alton Sterling, who was shot dead by police during an incident in Baton Rouge, Louisiana, on Tuesday.
What do we know about the two victims?
The 32-year-old had worked in the canteen of a school in St Paul for more than 10 years, his uncle Clarence told media in Minnesota. The JJ Hill Montessori Magnet School in the city listed Mr Castile as a cafeteria supervisor on its website.
On his Facebook page, Clarence later re-posted comments by a Minnesota bishop, Divar Kemp, calling Philando Castile "an a1 genuine man who was killed because he obeyed what the officer asked him".
Mr Castile's cousin, Antonio Johnson, told the Star Tribune newspaper his cousin had graduated with honours from St Paul Central High School.
Mr Castile was "a black individual driving in Falcon Heights who was immediately criminally profiled and he lost his life over it tonight", he said.
He added that Mr Castile was "very non-confrontational" and "a real upstanding citizen".
The Star Tribune said Mr Castile had only minor offences on his criminal record.
Little is publicly known about Mr Sterling, 37.
The father of five sold CDs and DVDs in the car park in which he died, family members told media in Louisiana.
"If you asked Alton for the shirt off his back, he'd give it to you," his aunt, Lorna, told The Advocate newspaper. "Alton would give you the world."
One broadcaster, 9News, said Mr Sterling had a long criminal record, that included several battery, drug, and burglary charges. It said he was also arrested in 2009 for resisting an officer and illegally carrying a weapon.
But Lorna Sterling said her brother had sought to earn a living after his last conviction in 2011.
Two black men have been shot dead by police in the US this week, the latest in a line of similar incidents, many of which have led to protests.