More than 20,000 Ukrainian refugees who fled after Russia's invasion reached the United States's southern border in April, an indication of the extreme measures many have taken to escape.

Across the U.S.-Mexico border, a total of 32,288 noncitizens sought admission at the ports of entry in April but lacked documents to enter. Of that number, exactly 20,059 were from Ukraine, according to a report released Tuesday by the Transactional Records Access Clearinghouse at Syracuse University in New York. Nearly all of the Ukrainians were allowed to enter the U.S. following the Department of Homeland Security's instruction that border officials make an exception for this specific population.

Ukrainians have been showing up at the southern border because many lack visas necessary to enter the U.S., and no refugee process is in place to accommodate large numbers of people coming in by plane. Mexico, though, does allow Ukrainians to enter relatively easily, leading many fleeing war and hardship to try to fly to Mexico and then show up at the U.S. border in hopes of submitting asylum claims. Most are allowed to enter the U.S. while their claims are processed and have a good chance of being allowed to stay.

Nearly all of them are flying to Tijuana, Mexico, which has a major airport, and then traveling just a few miles to San Diego.

“It’s generally easier for Russians and Ukrainians to obtain visas to travel to Mexico than to the U.S.," Jessica Bolter, U.S. immigration policy analyst for the Migration Policy Institute in Washington, told the Washington Examiner. "Mexico offers ... Ukrainians a special electronic visa for tourism purposes, which has less requirements than a tourist visa and can be completed online."

The increase in Ukrainian arrivals is a development immigration analysts predicted in conversations with the Washington Examiner at the onset of the war.

The increase in arrivals between Tijuana and San Diego began after the Biden administration told border officials in March that they may consider exempting Ukrainians from Title 42, a pandemic public health policy that requires all asylum-seekers and noncitizens to be immediately turned away. Since then, nearly all Ukrainians are being admitted and released into the U.S. under a procedure known as "humanitarian parole." Ukrainians may then seek asylum.

The 20,059 figure at the southern border is a significant increase from 3,155 in March and 184 in February, according to U.S. Customs and Border Protection data. The Ukraine-Russia conflict commenced Feb. 24 when Russian leader Vladimir Putin's military invaded the former Soviet republic.

234,088 MIGRANTS ENCOUNTERED AT SOUTHERN BORDER IN APRIL, MOST IN A CENTURY

Across all nationalities of people who showed up at the ports seeking admission nationwide, not just the southern border, Ukrainians made up roughly 30%, followed by Mexicans at 9% and Filipinos at 8%.

The number is extraordinarily high compared to entire recent years. In all of fiscal year 2021, which ran from October 2020 through September 2021, fewer than 700 Ukrainians sought admission at the southern border. In 2020, fewer than 100 were encountered.

"What we do on an individualized basis is evaluate whether a Ukrainian family and, frankly, other families from other countries qualify for our discretionary authority for granting humanitarian parole. Do they present to us an urgent humanitarian condition that requires special treatment? And that's not specific to Ukrainians. We apply that across the board," Secretary of Homeland Security Alejandro Mayorkas told CBS News host Norah O'Donnell on April 6.

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President Joe Biden vowed March 24 to receive as many as 100,000 Ukrainian refugees displaced by Russia's invasion. The Biden administration has urged Ukrainians to seek admission through legal channels online rather than traveling to the border.