Mexico has outpaced the Central American countries of Guatemala, Honduras and El Salvador to become the largest single source of migrants taken into custody along the U.S.-Mexico border, U.S. Customs and Border Protection officials said Thursday.

CBP acting commissioner Mark Morgan emphasized that overall migrant crossings continued to decrease for the fifth month in a row following a record spike in Central American families and children in May.

CBP took just more than 45,000 people into custody at and between ports of entry in October. Officials have welcomed the decline, which follows a historic influx in the spring overwhelmed border infrastructure and immigration authorities.

The October number still outpaces the 34,871 taken into custody a year ago, in October 2018. Those taken into custody include both migrants apprehended between official border crossings, and those “deemed inadmissible” after presenting themselves at a formal crossing.

Morgan credited the decline — 14 percent from September to October — to Trump administration initiatives aimed at deterring migrants from coming to the border.

Those policies have included efforts to bar non-Mexican migrants from requesting asylum at the U.S. border if they have not already requested asylum in countries they passed through on the way, as well as amplified cooperation from Mexican armed forces in preventing migrants from reaching the United States.

One of the major initiatives, the “Migrant Protection Protocols” has seen U.S. border authorities send nearly 50,000 migrants — nearly all of them Central American asylum seekers — back across the border into Mexico during the past year to await U.S. court hearings. The migrants often spend months in dangerous border cities, where human rights groups say they have been vulnerable to homelessness, kidnappings and other violence from drug cartels and criminals. The Trump administration says the program — also known as “Remain in Mexico” — has been an effective deterrence strategy.

Morgan, who characterized the reports of violence against migrants in border towns as “anecdotal,” said U.S. officials recently visited migrant shelters in Mexico and found that “the safety was okay,” saying that State Department officials who interviewed migrants told him that few expressed fears of violence. When asked about a specific case involving a mother and daughter who allegedly were kidnapped after being returned to Mexico under the program, Morgan reiterated that the shelters he saw appeared to be secure, and that anyone fearing violence has the option to try again to ask for protection at a U.S. port of entry.

The administration is unable to use the MPP program to remove Mexican asylum seekers, which analysts say could be fueling the demographic shift in migrant apprehensions. In El Paso, the administration is running a pilot program to expedite asylum claims.

A central aspect of President Trump’s immigration policy is his massive wall project, which aims to construct hundreds of miles of border barrier from Texas to California. But the administration has yet to construct any barriers where barriers did not already exist — thus far the “new” barrier has been replacing old fencing along 78 miles of the U.S.-Mexico border. Morgan said his agency and the U.S. Army Corps of Engineers has broken ground in the Rio Grande Valley of Texas to build what will constitute the first section of barrier in an area that didn’t already have one.

Morgan attributed the delays in the project to “judicial activism” by judges who he and other officials have accused of trying to block the administration’s agenda for political reasons. He also cited challenges of acquiring privately owned borderland — the administration has acquired just a tiny amount of the land it needs to complete the barrier in Texas.

Approximately 65 percent of migrants taken into custody during the 2019 fiscal year were children and family groups, the officials said, a trend that flipped last month, with single adults now representing about 65 percent of those arrested, a proportion more consistent with traditional migration trends.

U.S. authorities made more than 977,000 arrests along the southern border during the 2019 fiscal year that ended Sept 30. Officials on Thursday described it as “one of the toughest and most difficult” in the Border Patrol’s 96-year history.

CBP also recorded a “massive increase” in the seizure of illegal drugs last month, in what officials said they view as a sign of improved success in interdicting illicit shipments because they have been able to shift resources away from migrant families.

Morgan said methamphetamine produced in Mexican “super labs” is flooding into the United States. “We seized over 9,700 lbs. of methamphetamine — that’s up 90 percent over the same time last year,” Morgan said. “Make no mistake. If your city, town or state has a meth problem, it came from the southwest border.”

Nick Miroff contributed to this report.