A man trying to smuggle more than a thousands tablets of the 'ultra-deadly' fentanyl in his underwear -- disguised as oxycodone -- was stopped at the U.S.-Mexico in what authorities believe is the first time border authorities have intercepted the purposely mislabeled drug, U.S. Attorney Laura Duffy announced Thursday.

Sergio Linyuntang Mendoza Bohon, 19, of Tijuana, Mexico, was arraigned on one charge of unlawfully importing a controlled substance Thursday.

Court documents revealed Bohon tried to smuggled 1,183 tablets of fentanyl labeled as oxycodone and 5.4 grams of powdered fentanyl. Officials said they believe it is the first time they have caught counterfeit oxycodone tablets containing the "ultra deadly" fentanyl as they were being smuggled.

“Unsuspecting individuals who illegally purchase oxycodone could potentially die from the ingestion of what turns out to be fentanyl tablets,” said Duffy in a statement. “We are very concerned that these counterfeit pills could bring serious harm to users. Even minuscule amounts of fentanyl can have devastating consequences for those who abuse it or literally even touch it.”

Duffy said the smuggler's recent attempt to bring the hundreds of counterfeit pills into the U.S. raises serious concerns about the rise of the drug, which has lead to dozens of overdoses across California and at least 11 deaths, according to the Sacramento County Department of Health and Human Services.

"So if I'm sitting in my garage and I have my bag of fentanyl that I bought on the internet, there's probably not a lot of real measurement going on to, how will I know you would overdose on this amount of fentanyl, versus the person next to you," said DEA Agent Amy Roderick. "And I don't think they really care."

On Feb. 10, a Customers and Border Patrol (CBP) officer was interacting with Bohon at the pedestrian crossing when the officer spotted an unnatural looking bulge, Duffy said. At a secondary inspection, officers found the tablets hidden in his underwear.

Immigration and Customs Enforcement’s Homeland Security Investigations (HSI) Special Agents responded.

In a statement to officers, Bohon wrongly stated the tablets were oxycodone and said he was trying to smuggle them into the U.S. However, officials from the Drug Enforcement Administration Laboratory confirmed the pills were made of fentanyl.

In Sacramento, at least 11 people have died and dozens have overdosed as a result of consuming counterfeit prescription painkiller Narco tablets, which instead contained fentanyl.

"It's also easier to smuggle," said Roderick. "You don't need as much to get high. We're talking grains of this stuff as opposed to a gram of heroin, where you can use grains of this."

Fentanyl is 20 to 50 times more potent than heroin. In some parts of the U.S., fentanyl is replacing heroin, or those making the drug are mixing it in with heroin.

DEA investigations have found many Mexican drug cartels, including Sinaloa, have bought the drug from China.

"When it comes up through Mexico, it does come through San Diego," said Roderick. "We know it's not all destined for San Diego, that we don't have a huge market for it here, but again, they are mixing it into heroin and fraudulent prescription pills and so there are a lot of different ways to mask or make heroin strong, or to try and make more money."

Bohon will appear in court next on May 2 before U.S. District Judge Marilyn L. Huff for a motion hearing.

NBC 7's Liz Bryant contributed to this report.