WASHINGTON — The top US agency combatting drug trafficking warned on Wednesday of a surge of “mass overdose” cases involving drugs like cocaine spiked with deadly amounts of fentanyl.

In a letter to law enforcement authorities around the United States, the Drug Enforcement Administration cited seven incidents since January in which multiple people overdosed and died in the same location after unintentionally ingesting fentanyl, a synthetic opioid.

“In just the past two months, there have been at least seven confirmed mass overdose events across the United States resulting in 58 overdoses and 29 overdose deaths,” the DEA letter said.

“Many of the victims of these mass overdose events thought they were ingesting cocaine and had no idea that they were in fact ingesting fentanyl.”

The DEA cited one case on January 28 where 10 people on the same city block in the US capital Washington overdosed after ingesting crack cocaine laced with fentanyl. Nine of the 10 died.

On March 4 at a homeless shelter in Austin, Texas, 21 people overdosed and three died after taking crack cocaine and methamphetamine that included fentanyl.

Other such overdoses took place in southern Florida, Colorado, Nebraska, and  Missouri, demonstrating the breadth of the problem.

“Fentanyl is highly addictive, found in all 50 states, and drug traffickers are increasingly mixing it with other types of drugs — in powder and pill form — in an effort to drive up addiction and attract repeat buyers,” the DEA said.

It said traffickers are putting fentanyl in fake prescription pills like OxyContin, Percocet and Vicodin that are popular among drug abusers.

Fentanyl — which is cheap to make and is deadly in minute amounts — and other synthetic opioids were involved in two thirds of the 105,000 US overdose deaths in the year to October 2021, according to the DEA.

It told local law enforcement to assume that fentanyl is present in any drugs they come across.