WASHINGTON, Aug. 30 (Xinhua) --Democratic presidential nominee Joe Biden on Sunday condemned violence in Portland, Oregon after one man was fatally shot following clashes between rival protesters.

"The deadly violence we saw overnight in Portland is unacceptable. Shooting in the streets of a great American city is unacceptable. I condemn this violence unequivocally. I condemn violence of every kind by anyone, whether on the left or the right," Biden said in a statement. "And I challenge Donald Trump to do the same."

"We must not become a country at war with ourselves," the former U.S. vice president continued, while accusing his Republican rival, sitting President Donald Trump, of "fanning the flames of hate and division in our society and using the politics of fear to whip up his supporters."

"The job of a President is to lower the temperature. To bring people who disagree with one another together. To make life better for all Americans, not just those who agree with us, support us, or vote for us," he added. "Donald Trump has been president for almost four years. The temperature in the country is higher, tensions run stronger, divisions run deeper."

The remarks came a day after a motorcade of Trump's supporters drove through downtown Portland, Oregon's largest city, and confronted with people opposing police brutality and racial injustice. Local police have said they are investigating the reported deadly shooting of one of the pro-Trump protesters amid the skirmishes.

"It is still early in this investigation, and I ask everyone to give the detectives time to do their important work before drawing conclusions about what took place," Portland Police Chief Chuck Lovell said in a statement. "This violence is completely unacceptable and we are working diligently to find and apprehend the individual or individuals responsible."

In a string of tweets on Sunday, Trump fired off at Portland's Democratic Mayor Ted Wheeler, reiterating his "law and order" message, a central theme of his reelection bid.

"The people of Portland, like all other cities & parts of our great Country, want Law & Order," the president wrote. "Ted Wheeler, the wacky Radical Left Do Nothing Democrat Mayor of Portland, who has watched great death and destruction of his City during his tenure, thinks this lawless situation should go on forever."

Wheeler, in a press conference Sunday afternoon, criticized Trump's stance on racial justice, saying that "it's you who has not found a way to say the names of black people killed by police officers."

The shooting also came amid demonstrations in Kenosha, Wisconsin in the wake of the Aug. 23 police shooting of 29-year-old African American man Jacob Blake, which grew chaotic and violent at times when a teenager shot and killed two protesters.

"What we can never have in America -- and must never allow -- is mob rule," Trump said in his speech accepting renomination from the White House on Thursday. "In the strongest possible terms, the Republican Party condemns the rioting, looting, arson and violence we have seen in Democrat-run cities like Kenosha, Minneapolis, Portland, Chicago, and New York."

White House spokesman Judd Deere said on Saturday that the president will visit Kenosha "on Tuesday to meet with local law enforcement and survey damage from the recent riots."

Wisconsin Governor Tony Evers, a Democrat, sent a letter to Trump on Sunday, urging him to reconsider his trip to Kenosha.

"I, along with other community leaders who have reached out, are concerned about what your presence will mean for Kenosha and our state," Evers wrote. "I am concerned your presence will only delay our work to overcome division and move forward together."

In late May, George Floyd died after a white police officer kneeled on the 46-year-old African American man's neck for nearly nine minutes during an arrest in Minneapolis, Minnesota, which sparked nationwide demonstrations against what activists have described as police brutality and systemic racial inequality, as well as social unrest in some U.S. cities.

Biden has made race relations a pillar of his White House run in response to the movement, while Trump has focused on violent aspects of the demonstrations and doubled down on his support for police officers.

Massive demonstrations have recently returned to streets of Washington, D.C. On Saturday night, protesters clashed with police who deployed tear gas and sting balls to disrupt the crowds.