A US judge in Texas on Friday suspended the two-decade-old approval of the abortion pill mifepristone while a legal challenge proceeds, dealing another setback to abortion rights in the United States.

Adding to the volatile legal landscape around abortion, a federal judge in Washington state on Friday issued a seemingly conflicting injunction that prevented federal regulators from altering access to the same abortion drug.

The 67-page ruling by US District Judge Matthew Kacsmaryk in Amarillo, Texas, will not take effect for one week, in order to give the Biden administration a chance to file an emergency appeal, which the U.S. Department of Justice said it will do.

Kacsmaryk's ruling is a preliminary injunction that would essentially ban sales of mifepristone while the case by anti-abortion groups before him continues. The judge, who was appointed to the bench by Republican President Donald Trump, has not yet made a final ruling on the merits of the challenge.

However, in his ruling he found that the lawsuit is substantially likely to succeed. He said that the U.S. Food and Drug Administration had ignored risks in approving the drug.

"The Court does not second-guess FDA’s decision-making lightly," he wrote. "But here, FDA acquiesced on its legitimate safety concerns - in violation of its statutory duty - based on plainly unsound reasoning and studies that did not support its conclusions."

The case was brought by four anti-abortion groups headed by the recently formed Alliance for Hippocratic Medicine and four anti-abortion doctors who sued the FDA in November. They contend the agency used an improper process when it approved mifepristone in 2000 and did not adequately consider the drug's safety when used by girls under age 18 to terminate a pregnancy.

"By illegally approving dangerous chemical abortion drugs, the FDA put women and girls in harm’s way, and it’s high time the agency is held accountable for its reckless actions," said Erik Baptist of the Alliance Defending Freedom, which filed the case.