US 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 a feisty State of the Union speech on Thursday, went to the state's capital of 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.

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 terminology more commonly employed by Republicans.

Trump, who is pledging a crackdown on illegal immigration 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.

He slammed Biden for backtracking on his use of the word "illegal" to describe the Venezuelan suspect in the crime, saying, "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.

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.

The twin appearances in Georgia come days after Trump nearly swept the key Super Tuesday primaries, forcing out his last Republican rival, Nikki Haley.

Biden dominated in his own party's nominating contests. He and Vice President Kamala Harris plan to visit all the battleground states in coming weeks, his campaign said.

Georgia was long reliably Republican but has become more competitive.

Recent polls show Trump holding an edge there -- as they do in most of the swing states that may determine the outcome of the November election. 

Biden's campaign announced a $30 million "buy" of television commercials in the closely divided states of Michigan, Pennsylvania, Wisconsin, Georgia, Nevada and North Carolina.