More women and children from Central America illegally crossed into the United States in 2016 compared with two years ago, when President Obama ordered an emergency government response to address the escalating border crisis.

A total of 137,366 unaccompanied minors and families with children were apprehended by Border Patrol agents along the border with Mexico in fiscal 2016, which ended Sept. 30, an increase of several hundred from 2014, according to statistics released Monday by U.S. Customs and Border Protection.

The surge comes after a significant drop in 2015 and has reignited questions about the efficacy of the administration's immigration policies. The vast majority of those who have entered the United States illegally are from three Central American nations: Guatemala, El Salvador and Honduras.

Human rights groups have said that most of the immigrants are fleeing gang violence and organized crime in their homelands and deserve refugee status. But the Obama administration has said that the immigrants are eligible for deportation if they fail to win political-asylum protections in a U.S. immigration court.

"We are determined to treat migrants in a humane manner," Homeland Security Secretary Jeh Johnson said in a statement. "At the same time, we must enforce our immigration laws consistent with our enforcement priorities."

After the 2014 crisis, during which Border Patrol stations in Texas were overwhelmed by the influx of Central American women and children, Obama ordered a governmentwide response, which included $750 million in aid to the Central American nations, additional temporary shelters and more immigration judges to process the asylum cases.

The administration also created a program to allow asylum seekers to apply for legal protections in the United States from within their home nations, hoping to discourage would-be immigrants from making the often-dangerous journey north under the guidance of human smugglers.

So far, only a few thousand children have won refugee status through the new system.

Sen. Thomas Carper (D-Del.), ranking member on the Senate Homeland Security and Government Affairs Committee, traveled to Mexico, Guatemala and El Salvador last week to discuss the migration crisis with officials in those nations, his office said.

"Often we focus too much attention to the symptoms of problems rather than trying to fix the underlying causes," Carper said in a statement.

How to address the undocumented Central American immigrants has become an issue in the 2016 campaign. Democratic presidential nominee Hillary Clinton has suggested that she would consider a policy of not deporting undocumented immigrants who do not violate other laws. Republican nominee Donald Trump has said he would seek to deport most, if not all, of the estimated 11 million people living in the United States illegally.