INDIANA, Pa. -- A major drug sweep has put a big group of drug dealers from four counties behind bars, police said.

State police conducted an 18-month undercover investigation in Indiana, Allegheny, Cambria and Westmoreland counties.

The investigation led to the apprehension of 21 alleged dealers Monday on drug-related charges.

“The detail was arranged in an ongoing effort to counteract the recent spike in overdose deaths and artillery crimes associated with drug trafficking and addiction,” said Capt. George A. Kuzilla Jr.

The suspects were allegedly selling crack cocaine, heroin, prescription pills and marijuana.

Police are still searching for eight other suspects.