WASHINGTON, United States -- A federal judge in Texas overturned the two-decade-old approval of a safe and effective abortion pill on Friday, the latest volley in a conservative battle against reproductive rights in the United States.

If it stands, the ruling by a Donald Trump appointee would reverse permission granted by the Food and Drug Administration (FDA) for a drug widely used to terminate unwanted pregnancies.

The FDA and the Justice Department both filed appeals against the decision on Friday, with President Joe Biden pledging to "fight this ruling".

"The lawsuit, and this ruling, is another unprecedented step in taking away basic freedoms from women and putting their health at risk," he said in a statement.

But, in an illustration of how deep the fracture on abortion runs in US society, a judge in Washington state moments later ruled in a separate case that access to the drug must be preserved in more than a dozen states.

The dueling legal opinions, along with the appeals, means the issue is almost certain to end up before the Supreme Court.

The conservative-dominated panel last year overturned the landmark Roe v. Wade ruling that had enshrined a woman's right to abortion for half a century.

Reaction to the Texas ruling was swift.

Biden called it an ideological attack on women's rights and freedoms.

"The court... has substituted its judgment for FDA, the expert agency that approves drugs," he said. "If this ruling were to stand, then there will be virtually no prescription, approved by the FDA, that would be safe from these kinds of political, ideological attacks."

The president of the powerful American Medical Association, Jack Resneck, said that allowing judges to interfere in "extensive, evidence-based, scientific review of ... well-established FDA processes is reckless and dangerous."

Planned Parenthood, one of the largest pro-abortion groups in the United States, said the ruling by Judge Matthew Kacsmaryk -- a former conservative activist aligned with the religious right -- was an assault on science.

"We should all be enraged that one judge can unilaterally reject medical evidence and overrule the FDA's approval of a medication that has been safely and effectively used for more than two decades," said the group's president Alexis McGill Johnson.

Kacsmaryk's ruling came after a coalition of anti-abortion groups sued to freeze the national distribution of mifepristone.

While he stayed the FDA's 23-year-old approval, he also halted "applicability of this opinion and order for seven days" to allow time for appeals.

Anti-abortion groups hailed the move.

"Today's decision out of Texas is a win for the health and safety of women and girls," said Katie Glenn of Susan B Anthony Pro-Life America.

"The ruling reaffirms that pregnancy is not an illness and abortion is not health care. Finally the FDA is being held accountable for its egregious violation of its own rules."

'Judge-shopping'
The case landed in his court via what critics call "judge-shopping," in which plaintiffs take legal action in a district where the judge has a history of rulings that support their case.

Federal judges in the United States have a right to issue rulings that carry national legal force.

Opinion polls show a majority of Americans favor access to abortion.

But the issue is an explosive one for those on the right, especially evangelical Christians.

A number of Republican-dominated states have begun trying to restrict access to abortion, and have launched legal attempts to overturn what many believed was settled law.

The Supreme Court ruling last year was seen as a major victory for the movement.

But it has proved unpopular with the electorate.

Some observers said the Republican failure to capture the Senate in last year's midterm elections, along with their lackluster showing in the House, was at least partially the result of their support for the issue.

More than half of all abortions in the United States are performed with medication.

Mifepristone is one component of a two-drug regimen that can be used in the United States through the first 10 weeks of pregnancy.

It has a long safety record, and the FDA estimates 5.6 million Americans have used it to terminate pregnancies since it was approved.