The U.S. Customs and Border Protection (CBP) released video showing two smugglers bringing the children to the border barrier on the Mexico side and dropping two little girls, three and five years old, from the top of a 4-meter (14 foot) wall marking the U.S.-Mexican border.

CBP officers said Wednesday that the incident took place in the middle of the night.

"On Tuesday evening, a Santa Teresa agent utilizing camera technology observed a smuggler dropping two young children from the top of the approximately 14-foot-high (4-meter-high) border barrier," CBP said in a statement.

The children were taken to a CBP station in Santa Teresa, New Mexico to be evaluated by medical personnel, and then were transported to a local hospital as a precaution. CBP said the girls remain in the agency's custody.

"I'm appalled by the way these smugglers viciously dropped innocent children from a 14-foot border barrier last night," chief patrol agent Gloria Chavez said in a statement.

Chavez said U.S. agents are working with Mexican authorities to identify those responsible.

"If not for the vigilance of our agents using mobile technology, these two tender-aged siblings would have been exposed to the harsh elements of desert environment for hours," Chavez said.

The U.S. is facing an increase of migrant arrivals at the country's southern border, mostly Central Americans who say they are fleeing poverty and violence in their own countries.

Recently, there has been an average of 500 unaccompanied children crossing each day.

President Joe Biden's administration is facing growing pressure to confront the situation and criticisms about how the unaccompanied minors have been cared for while under U.S. government custody.

According to official statistics, the Department of Health and Human Services had 12,918 migrant children in their care as of Tuesday, while CBP was responsible for the care of another 5,285.