The Drug Enforcement Administration is warning of a "nationwide spike" in fentanyl-related mass overdoses as it says the drug is killing Americans at an "unprecedented" rate – deaths that top Republicans are tying to the ongoing crisis at the southern border.

"The DEA is seeing a nationwide spike in fentanyl-related mass-overdose events involving three or more overdoses occurring close in time at the same location," the agency said in a letter to federal, state and local law enforcement.

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The agency said there have been at least seven mass-overdose events, involving 58 overdoses and 29 deaths. The overdoses occurred in states including Colorado, Texas, Nebraska and Florida.

The agency said that many of the victims believed they were taking cocaine, and did not know that it was laced with fentanyl – a deadly drug that is 50-100 times more potent than morphine.

"Fentanyl is killing Americans at an unprecedented rate," said DEA Administrator Anne Milgram in a separate statement. "Already this year, numerous mass-overdose events have resulted in dozens of overdoses and deaths. Drug traffickers are driving addiction, and increasing their profits, by mixing fentanyl with other illicit drugs. Tragically, many overdose victims have no idea they are ingesting deadly fentanyl, until it’s too late."

Jan 31, 2019: Packets of fentanyl mostly in powder form and methamphetamine, which U.S. Customs and Border Protection say they seized from a truck crossing into Arizona from Mexico, is on display during a news conference at the Port of Nogales, Arizona. Courtesy U.S. Customs and Border Protection/Handout via Reuters (Reuters)

The agency cited Centers for Disease Control statistics that in a 12-month period ending in October, there were more than 105,000 drug overdoses – 66% of which were related to fentanyl and other synthetic opioids.

The drug is primarily trafficked via the southern border. More than 10,586 lbs of fentanyl were seized at the southern border in FY 2021 by Customs and Border Protection (CBP), up significantly from the 4,558 lbs in FY 2020 and 2,633 in FY 2019. Most of the amount seized is caught at ports of entry.

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A recent report by the bipartisan Commission on Combating Synthetic Opioid Trafficking said the source of fentanyl into the U.S. has evolved from 2014-2019, when most fentanyl came in from China via international mail. Now, the report said, it comes in from Mexico via the land border.

"The drug is manufactured in illegal laboratories there using precursors from Asia – mainly the [People’s Republic of China] – and is trafficked principally by land into the United States," the report said.

In its statement, the DEA said it is working to trace the overdoses back to local drug trafficking organizations and international cartels who it said are responsible for the surging domestic supply of the drug. It said that in the first months of 2022, DEA seized nearly 2,000 lbs of the drug.

House Republican Leader Kevin McCarthy linked the spike in deaths to the Biden administration’s handling of the crisis at the southern border and noted the decision announced last week to lift the Title 42 public health order -- which allows for the rapid expulsion of migrants at the border.

"President Biden has never prioritized the security of our nation’s border and, while his decision to eliminate Title 42 may appease his far-left political base, it will come at the expense of the health and safety of the American people," McCarthy said in a statement to Fox News Digital. "The opioid epidemic is real and it is devastating families across the country. And now Biden’s radical open border policies will only exacerbate this crisis causing more deadly fentanyl to flow into our neighborhoods."

McCarthy said that the elimination of Title 42 "will only make this problem much worse."

"President Biden cannot ignore this drug epidemic – he must take action to stop this unprecedented flow of fentanyl and implement House Republicans' solutions to fully enforce Title 42 and secure our southern border," he said.

The decision to end Title 42 sparked concern from both Republicans and moderate Democrats – who have warned that the order should only be ended with a sufficient plan in place. 

The Biden administration has said that it expects a significant influx of numbers in the months ahead, planning for numbers of up to 18,000 a day. However, it has repeatedly said that it is implementing a plan to deal with such an increase.

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DHS Secretary Alejandro Mayorkas on Friday said that DHS has "put in place a comprehensive, whole-of-government strategy to manage any potential increase in the number of migrants encountered at our border."

"We are increasing our capacity to process new arrivals, evaluate asylum requests, and quickly remove those who do not qualify for protection," he said in a statement. "We will increase personnel and resources as needed and have already redeployed more than 600 law enforcement officers to the border. We are referring smugglers and certain border crossers for criminal prosecution. Over the next two months, we are putting in place additional, appropriate COVID-19 protocols, including ramping up our vaccination program."