Immigration arrests along the U.S. southern border rose in May to the highest levels ever recorded, as growing numbers of migrants arrived from Turkey, India, Russia and other nations outside the Western Hemisphere, the latest U.S. Customs and Border Protection figures show. 

CBP made 239,416 arrests along the Mexico border last month, a 2% increase from April, according to the totals. The agency is on pace to exceed 2 million detentions during fiscal 2022, which ends in September, after tallying a record 1.73 million in 2021.

May is typically a busy month for illegal border crossings, but the latest figures indicate a diversifying migration wave that presents a significant logistical and political challenge for the Biden administration.

Many migrants seeking to reach the United States first fly to Mexico. Last month, the number of border crossers from India arrested by CBP jumped to 2,438, up 55% from April, the latest figures show. Authorities encountered 2,310 border crossers from Turkey, up 51%. The number of Russians increased 102%, to 3,394.

In a statement released late Wednesday, CBP Commissioner Chris Magnus warned migrants of the dangers posed by illegal crossings.

"As temperatures start to rise in the summer, human smugglers will continue to exploit vulnerable populations and recklessly endanger the lives of migrants for financial gain," he said. "The terrain along the Southwest Border is extreme, the summer heat is severe, and the miles of desert that migrants must hike after crossing the border are unforgiving."

Many of the migrants arriving from outside the Western Hemisphere are not sneaking through the desert, however. After landing in Mexico and traveling to the U.S. border, they typically cross the Rio Grande or walk through gaps in the U.S. barriers, then surrender to U.S. agents and request humanitarian protection, adding to a court backlog of about 400,000 pending asylum cases.

CBP figures show border crossers from Mexico, Central America, Cuba and Haiti also continued to arrive in high numbers in May. Authorities detained 19,040 migrants from Colombia, up 45% from April, an ally nation the Biden administration describes as one of its most important partners for a regional approach to migration management.

For comparison, authorities detained just 408 Colombians during the same period a year ago, in May 2021.

The composition of Central American migration is also shifting, the May data shows. Authorities also stopped 18,944 Nicaraguans last month, a record, and more than twice the number of migrants from El Salvador were taken into custody.

President Joe Biden's Republican opponents are campaigning on border security ahead of the November midterm elections, and polls show the administration receives poor ratings on the issue.

Biden campaigned for office promising to reverse many of the Trump administration's border-control measures and establish a system that would be orderly and humane. Instead the administration has struggled to cope with ever-growing numbers of illegal entries and federal court rulings that have halted Biden's attempts to modify the U.S. immigration system.

Of the 239,416 arrests, 222,656 were made by the Border Patrol between official ports of entry, topping the 220,063 arrests recorded in March 2000 that were the previous all-time high, statistics show.

Biden's attempt to lift the pandemic-era border restrictions known as Title 42 was enjoined in federal court last month, but the latest figures indicate the administration applied the policy to fewer than half the migrants taken into government custody in May.

The Title 42 measures allow CBP to quickly deport border crossers or return them to Mexico without giving them a chance to seek protection under U.S. asylum laws. The provisions require the cooperation of Mexican authorities, who generally do not accept returns of migrants who are not from Mexico or Central America.

The Biden administration says the rapid-return policy has inflated CBP enforcement figures because migrants returned to Mexico under Title 42 do not face the threat of U.S. prosecution, and typically attempt to cross again until they're successful.

In May, 25% of the migrants arrested by CBP had at least one immigration arrest during the previous 12 months, the agency said, compared with an average re-encounter rate of 15% during the 2014-to-2019 period.

Biden officials say the economic fallout from the coronavirus pandemic and instability around the world have put migrants on the move.

Last week at the Summit of the Americas, held in Los Angeles, the United States and other nations in the hemisphere signed the "Los Angeles Declaration," affirming a regional commitment to protecting vulnerable populations while improving border controls and immigration cooperation.

"We acknowledge that addressing irregular international migration requires a regional approach, and that ongoing health, social, and economic challenges of the pandemic exacerbate the root causes driving irregular migration, including the vulnerabilities of many migrants and their communities," the declaration stated.

Biden has tasked Vice President Kamala Harris with leading the administration's Root Causes Strategy, with billions of dollars in new investments for Central America's Northern Triangle region of Guatemala, Honduras and El Salvador.

The leaders of those countries skipped the Los Angeles summit, however, and the latest CBP figures show those three nations accounted for only 21% of the migrants who crossed the U.S. border from Mexico last month.