One in six people now call immigration the most pressing problem facing the U.S., according to a new Gallup poll. That's up sharply since June, when just 5 percent said immigration topped their list of concerns.

The issue has gained prominence as a surge in unaccompanied minors crossing the nation's southern border illegally has left the government struggling to process the caseload.

In the July poll, immigration is about even with dissatisfaction with government, the economy and unemployment as the most frequently named problems. The 12-point increase from June is the sharpest in the poll this year. The 17 percent of Americans citing immigration as the most important problem is the largest share doing so since 2006.

The poll has a margin of sampling error of plus or minus 4 percentage points.

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