EXCLUSIVE: Drug cartels and trafficking networks at the southern border are seeking to exploit the coronavirus crisis for their own profit, as the administration is seizing enormous amounts of deadly narcotics, the head of Customs and Border Protection (CBP) told Fox News.

“As for the cartels and drug trafficking networks, we know that there is no ‘day off’ for them,” Acting CBP Commissioner Mark Morgan told Fox News this week. “They continue to exploit the current health pandemic by attempting to move counterfeit products into our country, yet we continue to seize large amounts of dangerous and deadly drugs along our nation’s borders.”

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According to CBP figures, overall seizures of the four major drugs -- cocaine, fentanyl, heroin and methamphetamine -- were all up in April, including a 27 percent increase in methamphetamines, and a four percent increase in fentanyl.

Morgan, in response to written questions, gave examples of the work CBP agents and officers are doing amid the crisis to stop drugs coming across the border. On April 25, agents in Laredo, Texas seized 578 lbs. of meth in a construction materials shipment in a tractor-trailer driven by a Mexican citizen, while also in April 66lbs of meth and two pounds of fentanyl were nabbed in a car driven by a Mexican national in San Ysidro, California.

Morgan said that the battle against drug smugglers shows the importance of border security --- even as immigrant rights activists and international bodies have called for the easing of certain border security measures.

NUMBER OF MIGRANTS IN CBP CUSTODY AT BORDER PLUMMETS AMID CORONAVIRUS CRISIS 

“Effective border security is an intertwined and complex set of threats. We must understand who and what is coming across our borders, and we must have the ability and tools to prevent those people and goods from being introduced into the U.S. that could do us harm,” Morgan said. “Whether it’s illegal narcotics that killed 68,000 people last year or the threat of an infectious disease coming across our borders, it’s all equally important to our national security. Border security is more important now than ever.”

In addition to law enforcement at the border, cartels have also been facing other challenges to smuggling narcotics into the U.S. because the precursors used to cook drugs like methamphetamine, fentanyl, and other synthetic opioids come from China.

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It all forms part of a new set of circumstances that agents and officers at the border are having to adapt to. Morgan said he “could not be prouder” of the CBP workforce, and noted the great risks they face, even as CBP has made a number of operational adjustments to keep CBP safe. So far four CBP personnel have died of COVID-19.

“How can you thank someone enough, someone who risked their life to protect others? They did something greater than themselves,” he said. “There just aren’t enough words. They are the true heroes.”

Fox News' Stephanie Bennett contributed to this report.