OAKLAND -- Forty people affiliated with a drug gang based in Mexico and the Central Valley that does business in Oakland have been arrested, law enforcement authorities said at a news conference Wednesday.

Oakland Deputy Police Chief David Kozicki said 30 of these suspects were arrested on federal and state drug charges during raids conducted by more than 600 officers from multiple agencies at 32 locations Wednesday.

"We consider this a very successful operation," Kozicki said. "A lot of work went into this. It was a like building a Swiss watch…we are proud of the fact that it went off without a hitch…No one was injured."

The raids, Kozicki said, targeted some of the area's most notorious dealers.

"These are major heroin and cocaine dealers," he said. "They are what are known as 'weight dealers' in the City Of Oakland…We anticipate this will make a significant dent in our narcotics and narcotics-related violence problems."

Called Operation "Piece Out," the investigation had been underway for nearly two years and involved local and federal agents. Those arrested were being held on a variety of charges, Kozicki said, both state and federal.

"We have our homicide investigators involved in talking with some of the people arrested," he said. "We feel they may be involved in some of our recent homicides and narcotics-related violence."

Agents seized "firearms, cash and narcotics" during the raids. A number of children were also taken into care by Child Protective Services, Kozicki said.

Oakland Police Chief Wayne Tucker said 20 of those raids were conducted in Oakland, and most of the suspects are Oakland residents.

Scott Schools, the U.S. Attorney for Northern California, said 23 suspects were indicted by federal grand jury today but six remain at large.

U.S. Drug Enforcement Agency Special Agent in Charge Javier Pena said today's raids were the culmination of a two-year investigation that was initiated by the San Francisco police department.

"We identified a very dangerous cell operating in the Oakland area that had ties coming in from Mexico," Pena said.

Tucker said the drug gang was "very violent" and two persons of interest were murdered during the course of the lengthy investigation.

The investigation targeted a significant tar heroin trafficking organization, according to Oakland police Officer Roland Holmgren. Investigators believe the organization had the ability to distribute between 50 and 100 pounds of tar heroin monthly.

Tucker said "we've taken some very violent people off the street" and he believes Oakland residents are safer now that most of the suspects are in custody.

Authorities said the case was ongoing and more searches and arrests were possible.