(CNN) Roughly a dozen individuals who are not US citizens and are on the terror watchlist were encountered by federal officials at the US southern border from October 2017 to October 2018, according to an administration official familiar with data from Customs and Border Protection.

The number of individuals encountered at the southern border is a very small percentage of the total known or suspected terrorists who tried to enter or travel to the US in fiscal year 2017. That much larger number has been touted by the administration as it seeks to gain support to build a wall on the border.

The official adds there are not significant numbers of known or suspected terrorists crossing the southern border but the number went from "zero to a small increase" over the last couple of years.

But the official said that while the number of potential terrorists trying to cross the border is minimal, the Department of Homeland Security is concerned that terrorists could try to exploit immigration patterns.

It was not immediately clear how many US citizens who are on the terror watchlist were encountered at the border in the same period.

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