McALLEN, Tex. — The number of migrants crossing the U.S. southern border illegally has dropped more than 40 percent in the three weeks since President Biden announced broad restrictions on asylum claims, administration officials said Wednesday.

U.S. agents have taken fewer than 2,400 migrants into custody per day over the past week, down from more than 3,800 at the beginning of June, according to the latest Department of Homeland Security data. That is the lowest level of illegal crossings since Biden took office, DHS said.

The shift was evident Tuesday in the Rio Grande Valley of South Texas, which has been one of the border’s busiest migration corridors for the past decade. Along areas of the border where migrant families have crossed in large groups to surrender to U.S. authorities and seek protection, Border Patrol agents pursued a handful of adult men trying to evade capture. Agents’ radios were mostly quiet.

The Tucson area in the Arizona desert saw a similar decline in unlawful crossings, DHS Secretary Alejandro Mayorkas said during a news conference in that border city Wednesday.

“The president’s actions are working because of their tough response to illegal crossings,” Mayorkas said. “We are attacking the smuggling organizations that prey on the vulnerable even as the smugglers try to undermine our actions.”

It is not unusual for agents to see a short-lived decline in crossings whenever the government announces a major crackdown. Illegal entries soared to record levels late last year but have been trending downward over the past several months, in part due to more aggressive enforcement by the Mexican government.

Biden administration officials released the border data on the eve of the first debate of 2024 scheduled Thursday between the president, a Democrat, and the presumptive Republican nominee, former president Donald Trump.

Biden administration officials hope the falling numbers of migrants can blunt Republican criticism of the president’s border record.Polls consistently show high rates of disapproval with Biden’s handling of border security and immigration issues. The president has criticized Republicans for opposing a bipartisan bill that would have increased enforcement,leaving him to act on his own.

Homeland Security officials cautioned the results of the crackdown were preliminary, and cast the measures as an attempt to balance tougher enforcement with more generous opportunities for migrants to reach the United States legally.

Biden has “carried out the largest expansion of lawful pathways and orderly processes in decades,” according to a DHS fact sheet on the latest data,measures that are “freeing up the asylum system for those with legitimate claims.”

Republican lawmakers have urged Trump in recent days to target Biden’s immigration record, and have focused on migrants who commit crimes. Most migrants taken into custody at the southern border do not have criminal records, Customs and Border Protection data show.

“I hope President Trump confronts President Biden with this dangerous result of his open border policies at Thursday’s debate,” Sen. John Cornyn (R-Tex.) said on X Wednesday.

The American Civil Liberties Union and immigrant advocacy groups are suing to block Biden’s asylum restrictions,saying they are endangering people seeking protection.

The United Nations refugee agency has said it is also “profoundly concerned” that the new measures may deny access to asylum for people who are eligible for it.

U.S. immigration laws allow anyone who reaches U.S. soil to seek humanitarian protection if they have a well-founded fear of persecution in their home country. The emergency measures Biden announced June 4 suspend access to those protections on an emergency basis, arguing the U.S. immigration system is too overwhelmed by illegal crossings and insufficient resources.

Biden’s measures call for the asylum restrictions to lift if illegal crossings average fewer than 1,500 per day. They would return if the levels once more surpass 2,500 daily.

Lower number of illegal crossings have allowed U.S. agents to better safeguard the border and increase patrols, the department said, “enhancing DHS efforts to interdict individuals who pose a threat to public safety.”

The DHS statement echoed the administration’s calls for lawmakers to boost funding for the U.S. immigration system, including a major expansion of detention and deportation operations.

DHS said the number of migrants who are allowed into the United States with a pending court date after crossing illegally — the practice derided as “catch and release” — has dropped 65 percent under Biden’s measures. Deportations and returns to Mexico have doubled over the past three weeks, the department said.

Maria Sacchetti contributed to this report.