Washington (AFP) - The fight for abortion rights "isn't over," US President Joe Biden said Sunday, 50 years after a landmark Supreme Court ruling had guaranteed that right, before the court reversed itself last June.

"Today should've been the 50th Anniversary of Roe v. Wade," the Democratic president said on Twitter, referring to the original ruling.

"Instead, MAGA Republican officials" -- supporters of former president Donald Trump, with his Make America Great Again slogan -- "are waging a war on women's right to make their own health care decisions."

Since the Supreme Court overturned the Roe ruling -- a reversal made possible with the votes of three conservative justices appointed by Trump -- some 20 Republican-led US states have passed laws banning or severely restricting abortion rights.

Biden added: "I haven't stopped fighting to protect women's reproductive rights – and I never will."

In a weekend of competing demonstrations from the two sides of the heated national debate, some 300 women in New York demonstrated Sunday for abortion rights, chanting slogans -- including "My body, my choice" -- like those heard at the time of the original 1973 Roe ruling. 

And Vice President Kamala Harris, speaking in Tallahassee, Florida, joined the calls to protect abortion rights.

"How dare they?" she asked in an impassioned address before a group of abortion-rights advocates.

To loud applause, she assailed recent abortion-limiting laws passed by "extremists, including in states like Florida," adding: "We will not back down."

'Movement is recharging'

Florida, whose Republican governor Ron DeSantis is considered a rising star on the American right, now bans abortions after 15 weeks, with no exceptions for incest or rape.

One in three American women now live in a state that has imposed severe restrictions on abortion, according to Planned Parenthood, an abortion advocacy group and women's health provider.

"While what’s happening to patients and providers is devastating, our movement is recharging," the group's president, McGill Johnson, said at the event with Harris.

"Rain or shine, we will show up and keep fighting. Every. Single. Day."

Biden's own powers in this area are relatively limited, with the battle mostly going on now at the state level.

And anti-abortion groups, with strong support on the religious right, have not lessened their pressure.

Nationwide, thousands of them marched Friday to demand a nationwide abortion ban. 

Biden, in his series of tweets Sunday, said that "a woman's right to choose is non-negotiable," and he called on Congress to pass legislation codifying the abortion rights laid out in the Roe case.

But with Republicans now in control of the House of Representatives, the lower chamber of Congress, such legislation has virtually no chance of succeeding.

Since June, Biden has had to settle for issuing relatively limited orders, such as authorizing Veterans Administration hospitals to provide abortion services.

The White House also wants to protect access to mifepristone-based pills, which can be used to end a pregnancy in the early weeks.