Customs and Border Protection agents apprehended fewer than 12,500 people who illegally entered the U.S. from Mexico in March, making it the lowest monthly number in 17 years, according to written testimony from Homeland Security Sec. John Kelly.

The number of unaccompanied minors and family units who were taken into custody on land dropped sharply to 18,762 in February, the first full month of President Trump's administration, which Kelly said was a sign of decreased traffic of illegal immigrants. A total 23,589 illegal immigrants were detained in February including ports of entry near the southern border. It's unclear whether the 12,500 figure for March includes ports of entry numbers.

Last month, Kelly said the "unprecedented" drop from 31,578 apprehensions in January reflects a reduced flow of illegal immigrants, and indicates Trump's policies and executive actions on immigration - calling for a new border wall and follow-through of all immigration laws— are already causing some to stop before coming.

While apprehensions — or the number of illegal aliens taken into custody by border agents — tend to decrease during the winter months, CBP historically has seen a 10 to 20 percent increase from January to February.

Although illegal entrant numbers typically rise during the spring and summer months, Kelly added that the administration's early efforts to thwart these problems indicate continued action will have an effect in the coming months.

From February to March, apprehension numbers normally increase 10 to 30 percent.