Joe Biden warns ‘forces of darkness’ dividing US — and urges unity

White House hopeful Joe Biden warned on Tuesday that "the forces of darkness" are dividing Americans, stressing that as president he would strive to "end the hate and fear" consuming the nation.

In a speech at the site of the famous Civil War battle of Gettysburg, the Democratic challenger to President Donald Trump in November's election condemned the rise of white nationalism and said the country needed to unite.

"The forces of darkness, the forces of division, the forces of yesterday are pulling us apart, holding us down and holding us back," Biden said in a speech near where president Abraham Lincoln delivered his inspirational second inaugural address in 1865.

"We cannot and will not allow extremists and white supremacists to overturn the America of Lincoln and (abolitionists) Harriet Tubman and Frederick Douglass, to overturn the America that has been a haven and a home for everyone no matter their background," Biden added.

The 77-year-old, who leads in polling four weeks from election day, made no mention of Trump's name, but the Democrat's remarks notably came one week after the president failed to directly condemn white nationalism during their contentious debate in Cleveland.

Biden's speech was intended to serve as a call for unity after months of bitter divisions, but he also said he was "concerned" about what he sees today in America.

"The country is in a dangerous place, our trust in each other is ebbing, hope seems elusive," and politics is no longer a forum for mediating differences but a battleground for "total, unrelenting partisan warfare," he said.

"Instead of treating each other's party as the opposition, we treat them as the enemy. This must end," Biden added.