The number of unaccompanied children apprehended at the Southwest border between the U.S. and Mexico dropped nearly 20 percent in the fiscal year just ended, compared to the prior fiscal year, Customs and Border Protection announced Tuesday.

CBP said 48,861 unaccompanied minors, or foreigners under the age of 18, were apprehended or deemed inadmissible upon being taken into custody at or near the border in fiscal year 2017. That number was 59,692 in the prior fiscal year.

President Trump took office part-way through that fiscal year, and his push to secure the border has been credited with driving the number of attempted border crossings lower in many categories.

"We have seen historic low numbers this year — an almost 30 percent decline in apprehensions in FY17, but we are very concerned about the later month increases of unaccompanied minors and minors with a family member," said acting CBP Deputy Commissioner Ronald Vitiello.

The number of family units apprehended at the border ticked up from around 78,000 in FY 2016 to 105,000 in FY 2017, which ended in September.

Unaccompanied minors historically peaked during the summer of 2014, when more than 68,000 were documented arriving at the southern border.

The William Wilberforce Trafficking Victims Protection Reauthorization Act established minors who arrived at the U.S. border and were from noncontiguous countries receive special care and not be turned away as is standard procedure for adults.