US President Donald Trump has accused the Democrat mayor of Portland, Ted Wheeler, of allowing the “death and destruction of his city”. Mr Biden has stepped in to defend Mr Wheeler, saying the President was “recklessly encouraging violence”.
Saturday saw Portland divided between a pro-Trump rally and a Black Lives Matter demonstration that later clashed.
A man was shot dead on Saturday, culminating a day of unrest in the streets of Portland.
The city has become a hotspot for protests against police brutality and race inequality since a wave of demonstrations began on May 25, following the death of African-American George Floyd at the hands of Minneapolis police.
Mayor Wheeler issued a warning against visiting the city seeking revenge following a series of threatening social media posts.
In the tweets, he wrote: “For those of you saying on Twitter this morning that you plan to come to Portland to seek retribution, I’m calling on you to stay away.”
He also responded to Mr Trump’s comments on his reaction to the civil unrest.
He claimed it was the US President who had “created the hate and the division”.
On Sunday, Mr Trump posted a series of tweets, accusing the mayor of permitting “death” and “destruction” to take place in Portland.
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“We have only been there with a small group to defend our US Courthouse, because he couldn’t do it.
“The people of Portland, like all other cities & parts of our great Country, want Law & Order.
“The Radical Left Democrat Mayors, like the dummy running Portland, or the guy right now in his basement unwilling to lead or even speak out against crime, will never be able to do it!”
Joe Biden hit back a Mr Trump over his handling of the crisis as President.
In a statement, Mr Biden said: “[Trump] may believe tweeting about law and order makes him strong – but his failure to call on his supporters to stop seeking conflict shows just how weak he is.”
Earlier accusations by acting US Homeland Security Secretary Chad Wolf mirrored those of Mr Trump’s.
Mr Wolf said Democrat officials in Portland had allowed “lawlessness and chaos” to unfold.
He added that “all options” were on the table to respond to the crisis.