White House trade advisor Peter Navarro told CNBC on Friday that President Donald Trump's threat of new tariffs on Mexico is tied to the president's declaration of a national emergency at the border and came in response to Mexico's "export" of "illegal aliens."

In the first public defense of the president's move from a top trade official, Navarro also pushed back on the notion that the tariffs were intended to bring more manufacturing jobs to the United States from Mexico, saying that the tariffs were "not at all" related to that goal.

"This is strictly about national security and threats to our economy from illegal immigration from a criminal enterprise," Navarro said in the interview on "Squawk on the Street."

But in a series of tweets posted nearly simultaneously with Navarro's appearance, Trump wrote that "In order not to pay Tariffs, if they start rising, companies will leave Mexico, which has taken 30% of our Auto Industry, and come back home to the USA."

"Mexico must take back their country from the drug lords and cartels. The Tariff is about stopping drugs as well as illegals!" he wrote.

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In a surprise move, Trump announced Thursday night that the U.S. will slap escalating tariffs on Mexican imports, starting at 5% in less than two weeks, if the country does not take action to reduce unlawful immigration into the United States.

The legal justification for the move, Navarro said, was premised on the International Emergency Economic Powers Act, which requires a national emergency.

"Clearly we have that at the border," Navarro said.

"If you look at it from an investor's point of view and a corporate point of view, what we have in Mexico is the export, one of their high exports, of illegal aliens. And it's a criminal enterprise," Navarro said.

Trump declared a national emergency at the southern border in February after failing to secure funding from Congress for his proposed wall on the U.S.-Mexico border.

Markets tanked on Friday amid worries that the threatened tariffs combined with an escalating U.S.-China trade war could send the economy into a recession.

Navarro urged investors to look at the situation "calmly."

"Look at what we are trying to do. This is actually a brilliant move by the president to get Mexico's attention, to get them to help us, because so far they have just been standing by," Navarro said.

WATCH: The full interview with Peter Navarro