Former US Secretary of State Colin Powell has strongly criticised President Donald Trump's handling of anti-racism protests, saying he has "drifted away" from the constitution.
The Republican, a former top military officer, is the latest to condemn Mr Trump's response, including his threats to use the army to quell unrest.
He said he would vote for Democratic candidate Joe Biden in November's poll.
President Trump responded by calling Mr Powell "highly overrated".
Mr Powell, the only African American so far to have served as the chairman of the Joint Chiefs of Staff, has joined a growing list of former top military officials to have launched scathing attacks on President Trump.
It comes amid days of nationwide protests against racism and police brutality sparked by the death of African-American George Floyd in police custody in Minneapolis on 25 May.
On Sunday, nine of 13 Minneapolis City Council members pledged in front of hundreds of protesters to dismantle the local police department and instead create "a new model of public safety that actually keeps our community safe".
Meanwhile, security measures across the US were lifted as unrest started to ease. New York ended its nearly week-long curfew, and Mr Trump said he was ordering the National Guard to start withdrawing from Washington DC.
What did Colin Powell say?
Speaking on CNN's State of the Union on Sunday, Mr Powell said: "We have a constitution. And we have to follow that constitution. And the president has drifted away from it."
Referring to President Trump, the retired four-star general said: "He lies about things, and he gets away with it because people will not hold him accountable."
Mr Powell also said the president's rhetoric is a danger to American democracy and said, referring to this year's presidential election: "I certainly cannot in any way support President Trump this year."
He added: "I'm very close to Joe Biden in a social matter and political matter. I worked with him for 35, 40 years. And he is now the candidate, and I will be voting for him."
Mr Powell, who is seen as a moderate Republican, did not vote for Mr Trump in the 2016 poll.
In the interview, he also backed America's military leaders who had criticised Mr Trump in recent days.
Gen Martin Dempsey, Joint Chiefs of Staff chairman under Barack Obama, told ABC's The Week earlier on Sunday that the president's words had hurt relations between the US public and the military.
And former Defence Secretary James Mattis last week accused Mr Trump of deliberately stoking division, saying he "angry and appalled" by Mr Trump's handling of the protests.
What has the reaction been?
On Twitter, Mr Trump said Colin Powell was "a real stiff who was very responsible for getting us into the disastrous Middle East Wars", referring to the 1990-93 Gulf War and the US-led invasion in Iraq in 2003.
Colin Powell, a real stiff who was very responsible for getting us into the disastrous Middle East Wars, just announced he will be voting for another stiff, Sleepy Joe Biden. Didn’t Powell say that Iraq had “weapons of mass destruction?” They didn’t, but off we went to WAR!— Donald J. Trump (@realDonaldTrump) June 7, 2020
Mr Biden also took to Twitter to hit out at Mr Trump's handling of the protests, saying he had "callously used his [words as a president] to incite violence, stoke the flames of hatred and division, and drive us further apart".
Former Secretary of State Condoleezza Rice told CBS News' Face the Nation that she would like Mr Trump to "put tweeting aside for a little bit" and have a conversation with the American people.
"Not everyone is going to agree with any president, with this president, but you have to speak to every American, not just to those who might agree with you," she said.
More on George Floyd's death
What about the protests?
The unrest in the US has largely been replaced by peaceful worldwide demonstrations, with Black Lives Matter protests staged in European nations on Sunday.
In the city of Bristol in the UK protesters tore down a statue of Edward Colston, a prominent 17th Century slave trader.
On Saturday, huge peaceful rallies took place across the US, including in Washington DC, Chicago and San Francisco. There was even a protest in the Texas town of Vidor, once infamous as a stronghold of the Ku Klux Klan white supremacist group.
George Floyd, 46, died in police custody in Minneapolis on 25 May. Video showed him pinned to the floor, with a white police officer kneeling on his neck for almost nine minutes.
Officer Derek Chauvin has been dismissed and charged with murder. Three other officers who were at the scene have also been sacked and charged with aiding and abetting.
Mr Floyd's funeral is scheduled for Tuesday in Houston, his home city before he moved to Minneapolis.