The US Supreme Court on September 11 granted a request by President Donald Trump’s administration to fully enforce a new rule that would curtail asylum applications by immigrants at the US-Mexico border, a key element of his hardline immigration policy.

The court said the rule, which requires most immigrants who want asylum to first seek safe haven in a third country through which they travelled on their way to the US, could go into effect as litigation challenging its legality continues.

The court’s ruling handed a victory to Trump at a time when much of his immigration agenda had been struck down by lower courts.

The rule would bar almost all immigrants from applying for asylum at the southern border. It represents the latest effort by Trump’s administration to crack down on immigration, a signature issue during his presidency and 2020 re-election bid.

The American Civil Liberties Union (ACLU) and others who challenged the administration’s policy in federal court said it violates US immigration law and accused the administration of failing to follow the correct legal process in issuing the rule, which was unveiled on July 15.

Eight days after the rule went into effect in July, California-based US District Judge Jon Tigar issued a nationwide injunction blocking it.

Then began a back-and-forth between Tigar and the 9th Circuit, which scaled back the injunction so that the Trump rule was blocked in the border states of California and Arizona while in effect in Texas and New Mexico. Tigar ruled to restore the nationwide ban on September 9, but the 9th Circuit scaled it back again on September 10.

They were both trumped by Supreme Court, which will allow the asylum restriction to remain in place until the underlying legality of the rule is determined at trial.

The Trump administration issued the rule in an attempt to reduce the surging number of asylum claims primarily by Central American migrants who have crossed the US-Mexico border in large numbers during his presidency.

The rule would block nearly all families and individuals from countries like El Salvador, Honduras and Guatemala from entering the US as asylum seekers after crossing through Mexico. The rule would keep asylum protections for Mexican citizens.

The rule drew legal challenges including from a coalition of groups represented by the ACLU who accused the administration of pursuing an “asylum ban” and jeopardising the safety of migrants fleeing persecution.

In the administration’s request to fully enforce the rule, US Solicitor General Noel Francisco asked the Supreme Court to issue a stay blocking the injunction while litigation over the issue proceeds because the judge’s order interferes with the government’s authority to establish immigration policy.

The administration said the rule screens out asylum claims that are unlikely to succeed and “deters aliens without a genuine need for asylum from making the arduous and potentially dangerous journey from Central America to the US”.