The efforts by Republican-led state legislatures to pass restrictive laws, which the White House and civil rights groups say make it harder for Americans to vote, follow former president Donald Trump's false claim that he lost the 2020 election because of widespread election fraud.

Biden said voting rights in the United States are "under assault" with an intensity he had never seen before.

"It's simply un-American," he said on Tuesday while delivering a speech in Oklahoma during the 100th anniversary of the Tulsa race massacre.

"I'm asking Vice-President Harris to help these efforts, to lead them among her many other responsibilities. With her leadership and your support, we're going to overcome again... It's going to take a hell of a lot of work."

Harris said in a statement: "Our administration will not stand by when confronted with any effort that keeps Americans from voting...We must protect the fundamental right to vote for all Americans regardless of where they live."

Separately, Democrats in the Texas House of Representatives boycotted a legislative session late on Sunday, blocking a vote on an election reform bill critics say would put up barriers for black and Hispanic voters.

A vote on the measure is certain to pass the Republican-dominated house.

Fourteen other US states have enacted 22 laws this year that make it more difficult for Americans to vote, according to the Brennan Center for Justice.

Biden and Harris have also asked Congress to pass an election reform bill that would update voting procedures, and a bill that would prevent discriminatory changes to voting laws.

Australian Associated Press