U.S. officials along the border with Mexico processed migrants 183,503 times in July, as illegal crossings jumped by 33% after dropping to a two-year low in June despite record high heat levels, according to government statistics published Friday.

Border Patrol agents recorded 132,652 apprehensions of migrants who entered the U.S. unlawfully in between ports of entry in July, compared to nearly 100,000 such apprehensions in June. Moreover, U.S. immigration authorities processed 50,851 migrants at legal ports of entry, a record high, mostly under a system that allows asylum-seekers in Mexico to use a phone app to request appointments to enter the U.S.

The sharpest increase in unlawful crossings occurred in Border Patrol's Tucson sector, a sprawling and remote region that covers most of Arizona's border with Mexico and parts of the Sonoran Desert, where temperatures have reached 110 degrees every day this summer. Border Patrol recorded nearly 40,000 apprehensions there in July, a record for the sector.

Border Patrol apprehensions rose across several demographics last month, especially among families traveling with children, a population that poses significant operational challenges for U.S. officials due to legal limits on the detention of minors. Border Patrol agents processed more than 60,000 migrant parents and children traveling as families in between ports of entry last month, nearly doubling June's tally.

Apprehensions of single adult migrants stood at just over 62,000 in July, virtually the same level as June. Border Patrol also processed more than 10,000 unaccompanied children, nearly a 50% jump from June.

In a briefing with reporters on Friday, a Customs and Border Protection official said the increase in crossings along Arizona's border with Mexico is being driven by smugglers. The official called the influx in the Tucson sector "particularly challenging" and concerning, noting Border Patrol has seen a spike in the number of migrants in distress there.

"We have seen the human smugglers' attempts to direct migrants toward that, and advertising to people that it is somehow an area that they can expect greater success crossing into the country," the official said. "That is not true."

The official, who only spoke to reporters on condition of anonymity, said the administration is trying to reduce unlawful crossings by carrying out "higher" numbers of deportations of migrant adults and families. The official declined to provide specific deportation numbers.  

While migrant crossings jumped in July, they have not returned to the record levels seen in some months in 2022, when monthly Border Patrol apprehension peaked at over 220,000. July's tally of illegal border crossings is also 27% lower than in July 2022.

Still, the increase in illegal crossings threatens the Biden administration's migration management strategy, which it credited for the two-year low in apprehensions in June. The strategy relies on programs that allow tens of thousands migrants to enter the U.S. with the government's permission each month, and heighten asylum standards for those who fail to use these procedures and instead cross into the country illegally.

In July, nearly 45,000 migrants were allowed to enter the U.S. at ports of entry after securing an appointment through CBP One, the government app the Biden administration has tried to transform into the main portal to the U.S. asylum system. The administration is also allowing up to 30,000 migrants from Cuba, Haiti, Nicaragua and Venezuela with American financial sponsors to fly to U.S. airports each month.

Another Biden administration border policy disqualifies migrants from asylum if they enter the U.S. illegally, without first seeking legal refuge in other countries they travel through on their way to American soil.

While those subject to the asylum restriction can be swiftly deported, the policy has been mainly applied to a subset of single adult migrants, since the government lacks the necessary number of asylum officers to screen all those who ask for protection. It has also not been applied to many migrant families, since it is the Biden administration's policy not to detain migrant parents and children for longer than 72 hours.

In addition to the increase in migration, the Biden administration's border strategy faces another challenge: a number of lawsuits. Republican-led states are asking a federal judge in Texas to shut down the migrant sponsorship program, while advocates for migrants are asking a federal appeals court in California to have the asylum restriction invalidated.

Camilo Montoya-Galvez

Camilo Montoya-Galvez is the immigration reporter at CBS News. Based in Washington, he covers immigration policy and politics.

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