Authorities announced a record seizure of the deadly painkiller fentanyl and nearly 30,000 fake pills spiked with the substance at the Mexico border Saturday.

Members of the Mexican Army made the bust Aug. 19 at a checkpoint to enter the U.S. near San Luis Rio Colorado, Mexico. Authorities stopped a tractor trailer truck attempting to cross the border and found the drugs smuggled within grocery supplies, reports the Los Angeles Times.

Authorities seized a total of 140 pounds of pure fentanyl carrying an estimated street value of $1.2 million, according to estimates from the Drug Enforcement Administration. They also confiscated 29,000 pills spiked with the substance. Fentanyl is a painkiller roughly 50 to 100 times more powerful than morphine.

“All I can say is that this not a surprise, Tijuana is the main corridor for Mexican drug traffickers to smuggle fentanyl into the United States,” Mark Conover, deputy U.S. attorney in San Diego and head of an inter-agency fentanyl working group, told the Los Angeles Times. “All the indicators are that this load of fentanyl was destined for the city streets of the United States.”

Law enforcement blames fentanyl for the steep increase in fatal opioid overdoses that claimed an estimated 60,000 lives in the U.S. in 2015.

Dealers in the U.S and Mexican cartels are turning to China in greater numbers for shipments of fentanyl at a fraction of the price of heroin. It is then used to create roughly 20 times more doses out of a heroin batch, providing dealers with huge profits. Officials estimate more than 90 percent of heroin in the U.S. is flowing in from Mexico.

A bipartisan proposal in the Senate would give border agents the technology to screen for chemicals at U.S. entry points in an effort to target fentanyl shipments.

Democratic Sen. Ed Markey of Massachusetts and Republican Sen. Marco Rubio of Florida proposed the INTERDICT Act earlier this year and are renewing their call for support after a report released Tuesday showed fentanyl deaths are rising.

A recent investigation by STAT predicts the annual death toll from opioids will rise by roughly 35 percent between 2015 and 2027. Their analysis predicts up to 500,000 people could die from opioids over the next decade. The experts agree, even in a best-case scenario, the crisis will not visibly start to subside until after 2020.

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