Republican presidential candidate Donald Trump's campaign filed a complaint with the U.S. Federal Election Commission (FEC) on Tuesday, arguing that U.S. Vice-President Kamala Harris could not legally take over funds raised by U.S. President Joe Biden's re-election campaign.

Biden, the 81-year-old Democrat, was in a tight race with Trump, and endorsed Harris when he ended his re-election bid on Sunday. Harris quickly took control of Biden's campaign accounts and has since won pledges from a majority of the delegates who at next month's party convention will determine the nominee, according to her campaign.

The fight over the accounts, which had roughly $95 million US in the bank at the end of June, is part of a multi-pronged effort by Republicans to stymie Harris' bid to lead the Democratic ticket.

The Trump campaign argued that Harris undertook a "brazen money grab," according to the filing by David Warrington, the campaign's general counsel.

In the filing, which was shared with Reuters, Warrington said Harris was in the process of committing what he described as the "the largest campaign finance violation in American history."

Campaign claim to money likely secure: watchdog group

Saurav Ghosh, a lawyer at the Campaign Legal Center, a non-partisan watchdog group, has said that because Harris was already part of "Biden for President" as the vice-presidential candidate, her claim on the money should be secure.

In any case, election regulators are unlikely to resolve the issue before the Nov. 5 presidential election.

The FEC said they were unable to comment on unresolved enforcement matters.

Harris' campaign has said it had raised $100 million US since Sunday, when Biden stepped back from the campaign and endorsed her — exceeding Biden's remaining tally in just a few days. Her campaign brushed off the FEC complaint.

"Republicans may be jealous that Democrats are energized to defeat Donald Trump and his MAGA allies, but baseless legal claims — like the ones they've made for years to try to suppress votes and steal elections — will only distract them while we sign up volunteers, talk to voters, and win this election," said Harris campaign spokesperson Charles Kretchmer Lutvak.