White House trade adviser Peter Navarro on Friday said that President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE's threat to impose tariffs on Mexico over the flow of migrants should come as no surprise.

“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 on CNBC.

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He said the administration is asking Mexican officials to cut off the flow of migrants from Guatemala, many of whom trek through Mexico to reach the U.S. border. Navarro also called on Mexico to break up "transnational criminal organizations" that he said help facilitate illegal immigration.

Navarro also called on Mexico to assist the U.S. with its handling of asylum-seekers by keeping them on the Mexican side of the border.

“What’s happening now is Mexico, by being a bystander in this criminal enterprise, is imposing enormous costs on the United States," he said. "On our welfare system, on our criminal justice system.”

Trump said in a pair of tweets late Thursday that the U.S. will impose a 5 percent tariff beginning June 10 on all Mexican imports “until such time as illegal migrants coming through Mexico, and into our Country, STOP,” a goal that has never been achieved in recent history.

The tariff will increase by 5 percent each month until it reaches 25 percent "unless and until Mexico substantially stops the illegal inflow of aliens coming through its territory," the president said in an unusual, 1,004-word follow-up statement distributed by the White House.

White House aides on Friday sought to portray the president's move as clearly telegraphed through his frequent threats in recent months to take action on illegal immigration. They also attempted to downplay the potential impact of the tariffs.

“I would suggest to investors to look at this calmly. Look at what we’re trying to do," Navarro said. "This is actually a brilliant move by the president to get Mexico’s attention to get them to help us. Because so far they’ve just been standing by, and they really have the power to help us.”

Stocks opened with heavy losses on Friday, with the Dow Jones Industrial Average falling 249 points on the opening bell. Lawmakers in both parties have raised concerns with the specter of tariffs on Mexican imports, arguing it will ultimately harm American workers and consumers.

Mexico has emerged as the United States' biggest trading partner, replacing China at the top spot amid Trump’s ongoing trade war with Beijing.

White House press secretary Sarah Huckabee Sarah Elizabeth SandersSarah Sanders on Trump's reported war dead criticism: 'Those comments didn't happen' Sarah Sanders memoir reportedly says Trump joked she should hook up with Kim Jong Un McEnany stamps her brand on White House press operation MORE Sanders told reporters Friday that Trump has not spoken with Mexican President Andrés Manuel López Obrador, who has urged the president not to pursue the tariffs.

Sanders said the White House did not give Mexico advance warning of the announcement, but suggested it should not have come as a shock given Trump's rhetoric about the border.

"Anybody in this country, or frankly in the world, that says they’re surprised by this has been living under a rock and not paying attention," she said. "The president’s been crystal clear that we have to take action, we have to step up, we have to do more and we have to secure our border."