US President Joe Biden has condemned the assassination attempt on his predecessor Donald Trump in a primetime address from the White House, telling Americans that US politics must never be a "killing field".

Trump, the presumptive Republican nominee for president, was wounded in the ear after a gunman opened fire at a rally in Butler, Pennsylvania. One person was killed and two more were critically injured in the attack.

In the Oval Office address - just the third of his presidency - Mr Biden urged Americans to "take a step back" and warned that "political rhetoric in this country has gotten very heated".

"No matter how strong our convictions, we must never descend into violence," Mr Biden said in remarks that lasted just under seven minutes.

His short, but forceful, address largely went off without a hitch, amid ongoing scrutiny following a number of high-profile verbal slips.

In his primetime address, the president called on Americans to come together and warned that increasing political polarisation meant November's election would be "a time of testing".

Mr Biden and Trump remain locked neck-and-neck in opinion polls ahead of the election.

Speaking from behind the Resolute Desk, Mr Biden listed off a growing number of violent political acts that have taken place in recent years.

"We cannot, must not, go down this road again. We've travelled it before in our history," he said, citing shootings targeting congressional members in both parties, the assault on ex-House Speaker Nancy Pelosi's husband and the 6 January riots.

“In America we resolve our differences at the ballot box," he said. "At the ballot box. Not with bullets."

Saturday's attack left America reeling, as Trump was struck in the ear shortly after he began speaking in Butler, Pennsylvania.

In images beamed around the world, the 78-year-old could be seen with blood dripping from his ear and down his face, raising a defiant fist as Secret Service agents pulled him off stage and into a waiting car.

The gunman - identified by the FBI as 20-year-old Thomas Matthew Crooks - was shot dead at the scene by Secret Service agents. Law enforcement agents told the BBC's US partner, CBS News, that they discovered explosive materials in his vehicle nearby and at his home.

Officials say they are still investigating what motivated the attack. Crooks was a registered Republican who had previously donated $15 to a liberal campaign group in 2021, according to media reports.

Classmates described him as a quiet young man who was bullied throughout school. A local gun club near his home in Pennsylvania confirmed he had been a member.

In his speech, Mr Biden said he was praying for the family of Corey Comperatore, a 50-year-old former firefighter who was shot and killed - along with two others who were critically injured - during the rally. The father-of-two was killed while shielding his family from bullets as they whizzed past Trump and struck members of the audience.

Mr Biden called Mr Comperatore a "hero" who was killed "while simply exercising his freedom to support a candidate of his choosing".

Allies of Trump's have been quick to blame President Biden and his campaign for the attack, alleging that the top Democrat had sought to stoke fears about his rival's return to office.

"The central premise of the Biden campaign is that President Donald Trump is an authoritarian fascist who must be stopped at all costs," JD Vance - a Republican senator who is under consideration for the vice-presidential nomination - wrote on X, formerly Twitter.

President Biden avoided addressing those criticisms in his address on Sunday night, though his campaign has temporarily pulled attack ads against Trump.

The former president himself has sought to strike a conciliatory tone since the shooting, thanking his Secret Service detail for their quick actions and calling on citizens to "stand united" and to "show our True Character as Americans".

He arrived in Milwaukee on Sunday night for the Republican National Convention, where he will accept his party's nomination for president.

Trump is also expected to announce his running-mate. US media has reported that just three men are still under consideration for the vice-presidential slot: Florida Senator Marco Rubio, North Dakota Governor Doug Burgum and Senator Vance of Ohio.

In a news conference earlier on Sunday, the Secret Service said they had no plans to impose additional security measures around the convention, saying they were satisfied with existing arrangements.

The agency has come under scrutiny as to how Crooks was able to get so close to Trump, despite members of the audience reportedly pointing him out to police.