Atlanta, Georgia - President Joe Biden and presumptive White House challenger Donald Trump traded barbs Saturday on the key topics of age and immigration, as they targeted the battleground state of Georgia.

Biden, hoping to ride the momentum from his State of the Union speech on Thursday, went to Atlanta to mobilize Black and Hispanic voters.

He once again attacked his Republican predecessor, who has vowed to be a "dictator" for one day.

"When he says he wants to be a dictator, I believe him," Biden told a rally, highlighting US economic strength while promising action to cut costs in areas such as housing, health and education.

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In an interview with MSNBC aired Saturday night, Biden said he regretted using the term "an illegal" when referring to the killer of a nursing student last month in Georgia.

"I shouldn't have used 'illegal,' it's 'undocumented,'" said Biden, who has been criticized by progressives and members of his own party for using the dehumanizing terminology.

Trump, who is pledging a crackdown on migrants as a key plank of his campaign, talked at length during his rally Saturday about the slain student.

"Laken Riley would be alive today if Joe Biden had not willfully and maliciously eviscerated the borders of the United States," he told a crowd of supporters in Georgia's Republican-leaning northwestern corner.

"Biden should be apologizing for apologizing to this killer."

At his rally, Trump also pretended to be a stuttering Biden, mocking his 81-year-old opponent.

Biden's campaign launched a TV ad Saturday in which the president directly addresses his advanced age, a major concern among voters.

"Look, I'm not a young guy. That's no secret. But here is the deal. I understand how to get things done for the American people," he says in the spot.

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Trump's team quickly responded with a video message that starts with Biden's statement, followed by clips of the president stumbling, falling, or looking confused.

Georgia was so closely divided in the 2020 election – carried by Biden by fewer than 12,000 votes – that Trump infamously phoned a top state official to ask him to "find" a few thousand extra votes. Among his many legal woes, Trump faces criminal charges in Georgia of working to overturn the state's election results.

As recent polls show Trump holding an edge in the state, Biden also faces a revolt by large swathes of his base over his stance on Israel's brutal Gaza assault.

In a scene that has become more and more frequent over the past months, his speech in Atlanta was interrupted by protesters demanding he push for an immediate ceasefire and an end to US military support for Israel's relentless attacks, which have killed more than 30,000 Palestinians since the October 7 Hamas attacks.