US President Joe Biden on Sunday described the attack on Donald Trump as an “assassination attempt” and appealed for "national unity", a day after the shooting on the former president shocked the entire world.

Trump, 78, survived the attempt on his life on Saturday when a 20-year-old shooter fired multiple shots at him at a campaign rally in Pennsylvania, injuring his right ear.

The shooting, which left one spectator dead and two others critically injured, is being investigated as an attempted assassination. The male attacker was also shot and killed by a member of the Secret Service.

Biden addressed the nation on Sunday afternoon after receiving a briefing in the White House Situation Room by his top national security team.

“As I said last night, there is no place in America for this kind of violence or any violence for that matter," Biden said.

"An assassination attempt is contrary to everything we stand for as a nation. Everything. It’s not who we are as a nation. It’s not American. And we cannot allow this to happen,” he said.

“Unity is the most elusive goal of all, but nothing is more important than that right now. Unity. We’ll debate, and we’ll disagree, that’s not going to change. But we’ll not lose sight of who we are as Americans,” said Biden, who returned from his weekend vacation in Delaware at midnight.

Biden said the FBI is leading the investigation that is still in its early stages.

“We don’t yet have any information about the motive of the shooter. We know who he is. I urge everyone, everyone, please, don’t make assumptions about his motives or affiliations. Let the FBI do their job and their partner agencies do their job,” he said.

President Biden said that he directed an independent review of national security at the election rally in Butler town to assess what happened and asserted that he instructed this investigation to be thorough and swift.

“As this investigation continues, here’s what we’re going to do. First Mr Trump as a former president and nominee of the Republican Party already receives a heightened level of security. And I’ve been consistent in my direction of the Secret Service to provide him with every resource, capability and protective measure necessary to ensure his continued safety,” Biden said.

“Second, I’ve directed the head of the Secret Service to review all security measures, all the security measures for the Republican National Convention which is scheduled to start tomorrow,” he said.

“And third, I’ve directed an independent review of the national security at yesterday’s rally to assess exactly what happened. And we will share the results of that independent review with the American people as well," he said.

"And finally, I’ll be speaking more about this tonight at greater length from the Oval Office,” Biden said.

Biden said that he spoke to Trump, his November 5 presidential election opponent.

“I am sincerely grateful that he is doing well and recovering. We had a short but good conversation. Jill and I are keeping him and his family in our prayers,” he said.

“We also extend our deepest condolences to the family of the victim who was killed. He was a father. He was protecting his family from the bullets that were being fired. We are also praying for the full recovery of those who were injured,” he said.

Republican and Democratic leaders have condemned the attack on Trump.

Trump has said that he will attend the three-day Republican Party convention from Monday which will nominate him as the party's candidate in the presidential election.

Taking to his social media platform Truth Social, Trump said that he will be leaving for Milwaukee for the Republican convention, despite originally planning to delay his arrival there following the shooting, CBS News reported. PTI LKJ GRS GRS GRS

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