WASHINGTON - US President Donald Trump said Friday he has signed an immigration proclamation, an order that would help effectively ban migrants who cross the U.S. border with Mexico illegally from qualifying for asylum.

The Trump administration unveiled new rules on Thursday to sharply limit migrant asylum claims by barring individuals who cross the US southern border illegally from seeking asylum. People have to come into the United States at points of entry, Trump said before leaving for Paris.

“We need people in our country but they have to come in legally and they have to have merit,” Trump said. The plan, which invokes the same authority Trump used to justify his travel ban on citizens of several Muslim-majority nations, is likely to be quickly challenged in court. The Trump administration lost a court bid on Thursday, when a federal appeals court in California ruled that it must continue a program begun under former President Barack Obama that protects hundreds of thousands of illegal immigrants who were brought into the country as children, known as Dreamers.

Trump said the ruling on the Deferred Action for Childhood Arrivals (DACA) program was good news because now the administration can appeal the case to the US Supreme Court. The measures are meant to funnel asylum seekers through official border crossings for speedy rulings, officials said, instead of having them try to circumvent such crossings on the nearly 3200-kilometre border.

But the busy ports of entry already have long lines and waits, forcing immigration officials to tell some migrants to turn around and come back to make their claims.

The move was spurred in part by caravans of Central American migrants slowly moving north on foot but will apply to anyone caught crossing illegally, officials said on Thursday. It’s unknown whether those in the caravan, many fleeing violence in their homeland, plan to cross illegally.

Administration officials said those denied asylum under the proclamation may be eligible for similar forms of protection if they fear returning to their countries, though they would be subject to a tougher threshold. Those forms of protection include “withholding of removal” — which is similar to asylum, but doesn’t allow for green cards or bringing families — or asylum under the United Nations Convention Against Torture.

The announcement was the latest push to enforce Mr Trump’s hard line stance on immigration through regulatory changes and presidential orders, bypassing Congress. But those efforts have been largely thwarted by legal challenges and, in the case of family separations this year, stymied by a global outcry that prompted Trump to scrap them.

The new changes were likely to be met with legal challenges, too. Omar Jadwat, director of the American Civil Liberties Union’s Immigrants’ Rights Project, said on Thursday they were clearly illegal. “US law specifically allows individuals to apply for asylum whether or not they are at a port of entry. It is illegal to circumvent that by agency or presidential decree,” he said.

Curbing immigration has been a signature issue for Mr Trump, who pushed it hard in the days leading up to Tuesday’s midterm elections, railing against the caravans that are still hundreds of kilometres from the border. He has made little mention of the issue since the election but has sent troops to the border in response.

As of Thursday, there are more than 5600 US troops deployed to the border mission, with about 550 actually working on the border in Texas. The military is expected to have the vast majority of the more than 7000 troops planned for the mission deployed by Monday, and that number could grow.

Trump also suggested he’d revoke the right to citizenship for babies born to non-US citizens on American soil and erect massive “tent cities” to detain migrants. Those issues were not addressed by the regulations on Thursday. The administration has long said immigration officials are drowning in asylum cases partly because people falsely claim asylum and then live in the US. with work permits.

The asylum section of the Immigration and Nationality Act says a migrant is allowed to make a claim up to a year after arriving in the US, and it doesn’t matter how they arrive — illegally or through a border crossing. Migrants who cross illegally are generally arrested and often seek asylum or some other form of protection. Claims have spiked in recent years, and there is a backlog of more than 800,000 cases pending in immigration court. Generally, only about 20 per cent of applicants are approved.

Trump has long said those seeking asylum should come through legal ports of entry. But many migrants are unaware of that guidance, and official border crossings have grown clogged.  Officials have turned away asylum seekers at border crossings because of overcrowding, telling them to return later. Backlogs have become especially bad in recent months at crossings in California, Arizona and Texas, with some people waiting five weeks to try to claim asylum at San Diego’s main crossing.