Two Texas men have been sentenced to more than five years each in federal prison for transporting a massive amount of fentanyl in the U.S., apparently at the behest of Mexican drug traffickers.

Brandon Montoya, 24, of Kaufman and Felipe Rodriguez, 22, of McAllen each received 63-month prison sentences for possession of fentanyl with intent to distribute, the U.S. Attorney's Office for Louisiana's Western District announced Tuesday.

The men, who pleaded guilty in September, also were ordered to undergo five years of supervised release following their prison terms.

According to court documents, the two were driving on Interstate 20 in May 2018 when they were pulled over by a Louisiana state trooper. A search of the vehicle turned up 10 one-kilogram packages of pure fentanyl and a fentanyl derivative.

Montoya and Rodriguez told agents they had been in Mexico when they were approached about work and asked to drive to California to pick up the drugs for transport to Atlanta, where they would be paid for their services.

The men said they understood that the work required them to transport deadly narcotics.

U.S.Attorney David C. Joseph said the drug seizure and subsequent prosecution was part of the Department of Justice's ongoing fight against deadly opioids.

"These drugs are now the leading cause of accidental death in the United States — more than even car accidents," he said. "This case alone involved enough fentanyl to kill every person in the state of Louisiana."

Fentanyl, a synthetic opioid, is 80 to 100 times stronger than morphine and is sometimes added to heroin to increase its potency. Occasionally it's disguised as heroin itself, the U.S. attorney's office said.

Last year, three Houston-area residents were arrested in Ohio after federal authorities reportedly caught them attempting to mail an amount of fentanyl described as "enough to kill everyone in Toledo several times over."