WASHINGTON (AFP) - Democratic presidential nominee Joe Biden and running mate Kamala Harris launched a two-pronged attack on Thursday (Aug 27) against Donald Trump, saying the president is fuelling unrest over police brutality and racial injustice and has failed to protect Americans.

Mr Trump "refuses to even acknowledge there is a racial justice problem in America," Mr Biden said in a statement amid swelling social unrest after an African-American man, Jacob Blake, was shot in the back at close range multiple times by police in Wisconsin.

The shooting sparked nationwide rage and three nights of violence in the city of Kenosha. Tensions soared when two protesters were shot dead on Tuesday.

A white 17-year-old was detained on murder charges connected to the protesters' slayings, and Mr Trump announced he was sending federal forces to Kenosha to "restore law and order".

On Wednesday Vice-President Mike Pence warned people watching the Republican convention that they "won't be safe in Joe Biden's America".

Mr Biden shot back that the deadly violence did not occur on his watch, and won't during a future Biden presidency.

"The violence we're witnessing is happening under Donald Trump. Not me," Mr Biden said, adding that Mr Trump - who has yet to publicly address Blake's shooting - is turning a blind eye to the crisis.

"Instead of looking to calm the waters, he adds fuel to every fire. Violence isn't a problem in his eyes - it's a political strategy," Mr Biden said.

"And the more of it, the better for him."

With Mr Trump set to close out the Republican convention with a speech on Thursday night, Ms Harris sought to shine a light on racial injustice and police brutality.

"As vice-president Biden put it, the shots fired at Mr Blake pierced the soul of our nation," she told reporters in an address in Washington. "It's sickening to watch. It's all too familiar. And it must end."

Ms Harris said she would "always defend" peaceful protesters but they should not be confused "with those looting and committing acts of violence."

She also warned against citizens taking the law into their own hands, a veiled reference to the arrested teen.

"Make no mistake, we will not let these vigilantes and extremists derail the path to justice," Ms Harris said.

Ms Harris also went after Mr Trump for his handling of the coronavirus pandemic, saying the president showed "reckless disregard" by failing to take decisive action.

"President Trump got it wrong in the beginning. And then, he got it wrong again, and again. And the consequences have been catastrophic," she said.

"Donald Trump has failed at the most basic and important job of a president of the United States. He failed to protect the American people," she said.

Mr Trump is expected to speak on Thursday about his efforts to end the pandemic and revive the battered US economy.