Philadelphia police arrested 84 people and seized more than $100,000 worth of drugs in a citywide sweep this week, the department announced Friday.

The sweep also yielded 18 firearms, including a .40-caliber assault rifle, police said.

The operation is the third of its kind that police have conducted this year, said Capt. Tom Davidson, the commanding officer of the Narcotics Field Unit. But Monday's sweep was the first that focused on districts across the city, he said, instead of targeting a particular neighborhood.

Narcotics officers prepared for the operation for some time, Davidson said, identifying dealers through surveillance and undercover drug purchases to establish probable cause. Then the unit obtained search warrants before setting out across the city Monday.

Police arrested 77 adults and seven juveniles, they said, and seized marijuana, powder cocaine, heroin, and prescription pills - including oxycodone, Percocet, and Xanax - with more pills recovered than usual.

Davidson said the search also recovered a large amount of marijuana packaged in what he called a "unique style of jars" with different-color caps.