(CBS) – The Border Patrol says one of its agents rescued an infant and a toddler who were left alone by migrant smugglers in western Arizona’s Organ Pipe Cactus National Monument. A migrant in a group of border crossers arrested Thursday west of the Lukeville, Arizona, port of entry alerted an agent to the children’s location.

An 18-month-old was subsequently found crying and a 4-month-old was discovered face down and unresponsive. Both have received medical attention at a hospital and were released back into Border Patrol custody.

“Yesterday smugglers left two young children — an infant and a toddler — in the Sonoran Desert to die,” Tucson Sector Border Patrol Chief John Modlin said in a statement. “This is not just another example of smugglers exploiting migrants for money. This is cruelty.”

It was not immediately clear if the smugglers blamed for abandoning the children were among those arrested. Authorities did not release any details about the children, including their genders, what country they came from and the identities of their parents or guardians.

Organ Pipe Cactus National Monument stretches along the Mexican border in southwestern Arizona, a harsh, dry landscape studded with towering cactuses and other desert flora. It’s about 130 miles southwest of Phoenix.

Because of its remoteness, the 517-square-mile park is a favored crossing area for some smugglers. The human remains of suspected border crossers are often found in the area.

While the high temperatures at Organ Pipe Cactus National Monument regularly soar into the triple digits during the summer, they topped out Thursday in the 90s amid cooler monsoon weather.

The agent who found the children began first aid on the infant while waiting for medical technicians from the Border Patrol and the National Park Service to arrive.

An ambulance took the children to a hospital for additional medical attention. The children were later returned to Border Patrol officials, who were trying to urgently place them with the Office of Refugee Resettlement, which oversees the care of migrant children picked up in the U.S. without family.

The Border Patrol’s Tucson Sector says it has seen a 12-percent increase in unaccompanied children being smuggled across the border over the past fiscal year.

Overall, however, the U.S. has seen a decline in the number of legal and illegal border crossings over the past two months, according to federal data released two weeks ago.

During the pandemic, Title 42, also known as the “Remain in Mexico” policy, kept many migrants from legally crossing at the border — forcing them to wait in Mexico as their case was being processed. As a result, some people seeking to migrate to the U.S. resorted to other methods.

Illegal border crossings have, historically, always been dangerous for migrants. But within the past year, there have been several deadly incidents involving smugglers trying to get people into the U.S. In June, 53 people died after being left in a tractor trailer in Texas’ scorching heat. Two months earlier, more than a dozen migrants were hurt in a rollover crash in the same state.

The U.S. government has faced heavy criticism not only in the wake of such incidents, but also as it waived certain restrictions to allow both Afghan and Ukrainian refugees to enter the country.

In an interview with CBS News’ Camilo Montoya-Galvez earlier this month, Customs and Border Protection Commissioner Chris Magnus said the Biden administration is striving to create a “fair and equitable” system for asylum-seekers.

“Our goal certainly is to be able to process all vulnerable populations in a fair and equitable way,” Magnus said. “I think this is something that we’re going to continue to work towards. It can be very challenging, depending on the circumstances.”

Magnus acknowledged that migrants expelled to Mexico face “very difficult” conditions, but he said each nationality arriving to the U.S. southern border has “specific circumstances,” noting that Ukrainians are fleeing an armed conflict in their homeland.

“We’re talking about different populations from different countries with different needs who are going to need to be processed differently,” he said. “There are a lot of factors involved. What works for one population does not necessarily work for all.”