The U.S. Border Patrol in August arrested 52 percent more unaccompanied immigrant children and families at the southern border than in the same month in 2014, according to statistics published Monday and reported on by The Associated Press.

The statistics show that Border Patrol apprehended almost 10,000 unaccompanied immigrant children and families last month alone. In August 2014, Border Patrol said that 6,424 children and families were arrested, compared to 9,790 this August.

White House spokesman Josh Earnest told AP that the figures were a "surprising uptick" and a "concern" for the administration, but didn't offer an explanation.

"This is something that we take very seriously," Earnest said, according to the Washington Free Beacon. "It's something that the administration has been quite vigilant about over the last year and a half, and it's something that we're going to closely monitor in the months ahead."

The total number of border arrests for the entire year, however, has fallen some 50 percent compared to last year.

Since the beginning of the fiscal year in October, agents have arrested 35,000 children traveling by themselves and more than 34,500 people traveling as families, AP notes.

Just a year ago, border officials were overwhelmed by a surge of more than 68,000 unaccompanied children at the U.S.-Mexico border, with many attempting to flee from violence in their Central American home countries, as The New York Times reported.

The numbers have significantly declined since then but, for an unknown reason, they began to increase in July and August, even though this time of year historically sees lower border crossings compared to the spring.

Border expert Adam Isacson, a senior analyst at the Washington Office on Latin America, said the 4,632 unaccompanied children apprehended at the border in August was the highest number his organization has seen since they began keeping records in 2009.

"It could be a flash in the pan, but we are going up the trend line," he said, suggesting the numbers could indicate the start of another surge.