Washington (CNN) Nearly 35,000 individuals were arrested crossing the southern US border illegally last month, according to a source familiar with the latest arrest figures.

In June, 34,911 people were arrested -- down from 40,334 the previous month.

After seeing higher levels of illegal crossings this spring, the administration likely welcomed the news.

But though the Trump administration has made cracking down on illegal immigration a priority, including a policy that had at one point resulted in separating undocumented families, it is nearly impossible to attribute the decline to any specific policy.

Aside from last year, which defied most seasonal border crossing trends, there has consistently been a decline in crossings from May to June dating back to 2000. The size of the dip varies by year.

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