The number of people apprehended at the U.S.-Mexico border declined in June, breaking a six-month streak of dramatic increases and prompting the Trump administration to quickly - though cautiously - claim an early victory in its negotiations for stricter border enforcement in Mexico.

The number of unauthorized border crossers detained by the U.S. Border Patrol in June fell to 94,897, a 28% decline from May, according to Wednesday's data from U.S. Customs and Border Protection (CBP).

Apprehensions declined as summer temperatures climbed and Mexico ramped up its own border enforcement following an agreement with the U.S. to avoid a tariff President Donald Trump threatened to levy.

"What we see in June is that our strategy is working. The president's engagement with Mexico, the deal to enforce immigration security on their southern border ... that's clearly having an impact on the flow," acting Homeland Security Secretary Kevin McAleenan told CNN on Tuesday, hours after his agency released preliminary estimates for June.

Reasons behind fluctuations

Migrants from Central America's Northern Triangle countries - El Salvador, Guatemala and Honduras - make up the majority of apprehensions. However, migration numbers fluctuate for various reasons, including changes in season, political climate, policy and weather.

In part, "we generally do have a small decline in June due to the high summer temperatures," a senior CBP official told reporters, acknowledging that there may be more than one factor causing last month's decrease in apprehensions.

The official added that the agency is "very optimistic ... as Mexico continues to deploy resources to their southern border and continues to beef up their border security."

The number of apprehensions at the U.S.-Mexico border usually reaches a peak in March, before declining steadily over the summer months. But this year, that reversal did not happen. Instead, that number spiked in May to more than 132,000.

"The logistics of this flow is different than the U.S. has ever seen. And the size is different than Mexico has ever seen," Andrew Selee, president of the Washington-based Migration Policy Institute, told VOA.

The drop in apprehensions from May to June shows "clearly there's an effect of Mexico's enforcement policies," Selee said. "Is the Mexico enforcement policy coherent? No. They threw together an enforcement response to stave off the threat from the Trump administration. It's had a dissuasive effect - but only so far."

In the wake of the tariff threat, Mexico deployed members of its newly formed National Guard - more like a national police force than a military branch - to its northern and southern borders to curb the passage of migrants.

The senior CBP official who spoke to reporters Wednesday said Mexican forces have been able to reduce the number of travelers in large groups attempting to cross into the U.S. In one case, the official said, "instead of having 200 [unauthorized border crossers] to deal with, we ended up having approximately 60 apprehensions."

Migrant children

Families and unaccompanied children still make up the majority of unauthorized border crossers, a senior CBP official told reporters during a media call Wednesday.

For years, single adults - largely men - made up the bulk of apprehensions, at a time when agricultural, seasonal work was a major draw. But that has changed over the years, and in 2019 in particular.

U.S. border detention centers were ill-equipped to handle the changed demographics. In recent months, media reports, activists, lawyers and the government's own internal investigators have criticized the quality of care for those in Border Patrol custody, especially in facilities for children.

From a peak in late May of more than 2,500 children held by CBP, the agency now has around 200, the senior official told reporters.

The children are being transferred to the U.S. Department of Health and Human Services, the agency tasked with caring for unaccompanied minors until their immigration or asylum cases are adjudicated, or until suitable guardians are located.

U.S. lawmakers will again question the acting DHS secretary in a hearing on July 12 over border policies and the treatment of detained migrants.