Washington DC - A year after the US Supreme Court scrapped the constitutional right to abortion in the United States, President Joe Biden on Saturday vowed to fight against the "extreme and dangerous" effort by Republicans to curb access to the procedure nationwide.

The high court's decision to overturn the landmark Roe v. Wade ruling passed the regulation of abortion back to individual states – some of which have since moved to drastically restrict the procedure.

"State bans are just the beginning," Biden said in a statement on the anniversary of the ruling. "Their agenda is extreme, dangerous, and out-of-step with the vast majority of Americans."

Pro- and anti-abortion groups were holding rival events in the American capital on Saturday, and Vice President Kamala Harris spoke about the health care "crisis" regarding reproductive rights in a speech in the southern state of North Carolina.

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Some 20 states, mostly in the South and Midwest, have prohibited abortion outright or severely restricted access while others, mainly on the coasts, have moved to protect it.

The closure of abortion clinics in about a dozen states has forced tens of thousands of women to travel elsewhere to terminate a pregnancy.

Biden also warned that Republicans were working to enact a nationwide abortion ban.

"Congressional Republicans want to ban abortion nationwide, but go beyond that, by taking FDA-approved medication for terminating a pregnancy, off the market, and make it harder to obtain contraception," the president said, referring to the Food and Drug Administration.

At one small rally in Washington, protesters carried signs and T-shirts bearing phrases like "I am the post-Roe generation," and "Unborn Lives Matter," urging national-level restrictions on abortion.

Steve Karlen, an anti-abortion campaigner, and his wife, Laura, traveled to the capital from the Midwestern state of Wisconsin to "celebrate" Roe's reversal, which also fell on their wedding anniversary.

"It's a blessing to have the abortion decision going back to the states," said Laura, a stay-at-home mother to five children. "But ultimately what we want is the unborn children to be protected (nationally) – that everyone in our country will have the right to live."

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With a divided US Congress, there is little Biden can do. Still, he said he would push for federal-level protections.

"My Administration will continue to protect access to reproductive health care and call on Congress to restore the protections of Roe v. Wade in federal law once and for all," he said.

Abortion rights proved a key issue for Democrats in the 2022 midterm elections, and are likely to be just as important in the 2024 presidential race.

They've also become an animating feature in Republican campaigns. Primary candidates are currently trying to outflank former president Donald Trump, the current frontrunner for the party's nomination, who has been criticized for flip-flopping on his position.

Speaking in Washington on Friday, Florida Governor Ron DeSantis hailed the six-week abortion ban he signed into law in his state, while ex-vice president Mike Pence challenged every candidate to back a nationwide prohibition.

"It was the right thing to do – don't let anyone tell you it wasn't," DeSantis said in a veiled swipe at Trump, who has criticized the Florida law as "too harsh."

The same day, Biden won the endorsement from the nation's leading abortion-rights groups, including Planned Parenthood, NARAL, and Emily's List.