President Donald Trump and Democratic rival Joe Biden have been accusing one another over violence that has erupted at protests in Portland, Oregon.
A man linked to a right-wing group was killed on Saturday, as elsewhere in the city a pro-Trump rally clashed with Black Lives Matter protesters.
Mr Trump called participants of the rally “great patriots” and blamed the city’s Democratic mayor for the unrest.
Mr Biden in turn accused Mr Trump of “rooting for chaos and violence”.
In a campaign speech in the city of Pittsburgh on Monday, the Democratic candidate said: “Fires are burning and we have a president who fans the flames rather than fighting the flames. But we must not burn. We have to build.”
Portland has become a flashpoint for demonstrations against police brutality and racism since the police killing of African-American George Floyd in Minneapolis on 25 May triggered a wave of national and international outrage.
Media reports say a man who calls himself an anti-fascist is being investigated over Saturday’s deadly shooting, while the founder of the right-wing group Patriot Prayer identified the victim as a supporter.
Mr Trump on Sunday re-tweeted what appeared to be the dead man’s name along with the message “Rest in Peace”.
Police have not publicly named the suspect or the victim, or specified whether the shooting was directly linked to the clashes.
The president is set to visit the city of Kenosha, Wisconsin, on Tuesday amid anger there over the police shooting of black man Jacob Blake.
Security: What have Trump and Biden said?
Mr Trump has blamed Portland’s Democratic Mayor Ted Wheeler for the unrest.
“Portland will never recover with a fool for a mayor,” he wrote on Twitter on Sunday as he suggested sending federal forces to the city.
He also accused Mr Biden of being “unwilling to lead”.
Mr Trump continued on Monday, describing Portland as “a mess” and repeating calls for “LAW & ORDER.”
“If this joke of a mayor doesn’t clean it up, we will go in and do it for them,” he wrote.
In another tweet he said “Radical Left Mayors & Governors of Cities where this crazy violence is taking place have lost control of their ‘Movement’.”
“It wasn’t supposed to be like this, but the Anarchists & Agitators got carried away and don’t listen anymore – even forced Slow Joe out of basement,” he added in reference to his Democratic rival.
On Sunday Mr Biden said the president “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”.
He continued the argument in his speech in Pittsburgh on Monday, where he said Mr Trump had “fomented” violence in US cities.
He called Mr Trump “a bystander in his own presidency” and “an incumbent president who makes things worse not better”.
“Donald Trump has been a toxic presence on our nation for four years,” Mr Biden said. “Poisoning how we talk to one another. Poisoning the way we treat one another. Poisoning the values this nation has always held dear. Poisoning our very democracy.
“Will we rid ourselves of this toxin or make it a permanent part of this nation’s character?”
Mayor Wheeler has also hit back at Mr Trump’s criticism, saying the US president had “created the hate and the division”.
“I’d appreciate it if the president would support us or stay the hell out of the way,” he added.
Law and order is a major theme of President Trump’s bid for re-election, as he seeks to paint the Democrats and their candidate as soft on crime. The Democrats accuse Mr Trump of trying to stoke tensions for political gain.
Security: What happened on Saturday?
Unrest broke out in Portland on Saturday night as a caravan of hundreds of Trump supporters clashed with Black Lives Matter protesters.
Portland police said they “heard sounds of gunfire” and “located a victim