Democratic presidential candidate Joe Biden's political campaign has asked social media giants Facebook and Twitter to remove posts by Republican President Donald Trump on Monday that it said made false claims aimed at discrediting mail-in voting.

Trump tweeted several times on Monday criticizing vote-by-mail plans that numerous states have implemented so that voters concerned about the coronavirus infection can submit their ballots from home.

"If people can go out and protest, riot, break into stores and create all sorts of havoc, they can also go out and VOTE - and keep our Election Honest," Trump wrote. "With millions of mail-in ballots being sent out, who knows where they are going, and to whom?"