San Francisco, California - A de facto ban on claiming asylum at the US southern border implemented in May in an effort to stop arrivals of migrants can stay in place for now, a court said Thursday.

A rule change earlier this year made it all but impossible for most migrants to lodge an asylum claim when crossing by land from Mexico.

President Joe Biden's administration said claims would still be accepted, but only if made in a migrant's home country or in a country they had passed through on their way to the United States.

The change came as Washington sought to untangle years of using Title 42, a public health measure that effectively prevented any undocumented person from entering the country, which was implemented as Covid-19 swept the world.

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Critics, including the American Civil Liberties Union (ACLU) charged the provision was illegal, and went to court to seek its reversal.

Last month, Judge Jon Tigar of the US district court in San Francisco said the policy was "unlawful," but he suspended his ruling for 14 days to give the administration time to appeal.

On Thursday, the Ninth Circuit Panel stayed that July 25 ruling, pending the outcome of the Biden administration's appeal.

The panel said it would expedite the process and ordered submissions by August 24.

"The stay ruling doesn’t say anything about the legality of the ban, and we are confident that we will prevail when the court has a full opportunity to consider the claims," said Katrina Eiland, deputy director of the ACLU’s Immigrants’ Rights Project.

"We are pleased the court placed the appeal on an expedited schedule so that it can be decided quickly, because each day the Biden administration prolongs its efforts to preserve its illegal ban, people fleeing grave danger are put in harm’s way."

When it filed its appeal last month, the Department of Justice said the new border rules were "a lawful exercise of the broad authority granted by the immigration laws."

The administration had fretted that up to 200,000 people would try to cross into the country every month once Covid rules lapsed.

Under the new provisions, migrants at the border have to use a smartphone app to obtain an interview appointment, which can take weeks or months.

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Those elsewhere have to request asylum from their home country or at special centers in countries they pass through.

People who cross the border without going through the process automatically lose the chance to claim asylum.

The policy raised the burden of proof for the applicants and left them facing long waits for rulings.

It, however, did create exceptions for unaccompanied children crossing the border, and for citizens of certain countries like Haiti and Ukraine offered a separate formal parole process.

The change had a quick impact: the number of border patrol interdictions or "encounters" with migrants fell from 212,000 in April to 145,000 in June, according to Customs and Border Protection figures.