U.S. border agents arrested or stopped nearly 1 million undocumented migrants at the southern border with Mexico in the last 12 months, the most in more than a decade, a top U.S. official said Tuesday. Despite record high numbers of crossings this Spring, the Trump administration said arrests at the U.S.-Mexico border fell in September for the fourth month in the row, and credited cooperation from Mexico and Central American countries in cracking down on migrants. Mark Morgan, acting commissioner of the U.S. Customs and Border Protection (CBP), said at a press conference that there were just over 52,000 migrants either apprehended or encountered at the southwest border in September, down almost 65% from a peak in May of 144,000. That monthly total is still the highest September level since at least 2014, according to CBP statistics.

The surge came amid President Donald Trump's tough efforts to halt illegal immigration, which began to show results only in the last three months, when border arrests plummeted. The Trump administration has stepped up efforts to discourage an exodus from Honduras, Guatemala and El Salvador by asking Mexico to impede their transit and requiring them to apply for asylum in the first country they enter, meaning either Guatemala or Mexico.

Besides restricting the ability of migrants to claim asylum, the White House has pressed forward on erecting more wall along the 3,200-kilometer border, diverting Defense Department funds committed to other programs for wall construction after Congress declined to provide the budget. Morgan said 114 kilometers of new barrier had been built and predicted that a total of 724 kilometers would be completed by the end of 2020.

Immigration has been a central issue for President Trump, who is gearing up to push it in his 2020 re-election campaign. His administration has taken a series of escalating measures to curb access to asylum and limit legal immigration. Many have drawn legal challenges. In September, the U.S. Supreme Court allowed a controversial new rule to take effect, one that could curtail most asylum applications at the border while the court battle over its merits continues.

The drowning of a Salvadoran father and toddler at the U.S. border in June highlighted the ongoing suffering of asylum-seekers making the dangerous journey to the U.S. to flee poverty and conflict. The photo was reminiscent of past failures to address the issue of migration in countries across the globe. Mexican newspapers compared the photograph to the 2015 image of the 3-year-old Syrian boy Alan Kurdi whose body washed up on a Turkish beach in 2015 while on the asylum journey across the Aegean Sea to Europe. In addition, the volume of people attempting to cross the borders vastly strained resources and prompted an outcry over fetid conditions at border stations where families and children were held for days and weeks at a time in facilities meant to hold them for a maximum of 72 hours.