Former US president Donald Trump vowed to end the Russia-Ukraine war if re-elected.

"I would have a peace deal negotiated within 24 hours," he said while campaigning for the 2024 US presidential elections in Columbia, South Carolina.

"We are at the brink of 'World War Three,'" Trump warned.

He warned that the next election would be America's last chance for salvation as he attempted to revive a faltering third run for the White House in two US states that launched his winning 2016 presidential campaign.