WASHINGTON, April 20 (Reuters) - U.S. President Joe Biden may announce his re-election campaign by video as soon as Tuesday, two people familiar with the matter said on Thursday, setting the stage for a possible rematch with his Republican predecessor Donald Trump.

A Tuesday announcement by Biden, 80, would come four years to the day after his 2020 campaign launch. One of the sources on Thursday cautioned that the exact timing could change.

"We'll announce it relatively soon," Biden told reporters last Friday of his campaign announcement. "I told you my plan is to run again."

Biden is the oldest person to have occupied the White House and would be 86 at the end of a second four-year term. He has struggled with low public approval ratings, with a Reuters/Ipsos poll completed on Sunday showing that just 39% of Americans approve of his job performance.

The White House and the Democratic National Committee declined to comment on the timing of the announcement.

Republicans have not yet picked their candidate for the Nov. 5, 2024, presidential election, but polls show Trump leads a pack of declared and undeclared Republican candidates that include Florida Governor Ron DeSantis, former Vice President Mike Pence and former UN ambassador Nikki Haley.

While Biden faces little serious competition for the Democratic nomination, 45% of Democrats responding to a March Reuters/Ipsos poll said they thought he should not run again in 2024, with 48% saying he should.