FLAGSTAFF, Ariz. (AP) – Nearly two dozen people have been charged with dealing methamphetamine on and around the Navajo Nation, a distribution network that authorities said is unparalleled on the reservation.

Federal, tribal and local law enforcement officials announced the arrests Thursday of 16 people and said six others have been charged in a yearlong investigation. They said the supply line for the dangerous drug stretched from Tuba City to the Phoenix metropolitan area with connections to Mexican drug cartels.

“We believe in taking this action we have broken key links in the supply chain to the Navajo Nation,” Arizona U.S. Attorney Dennis Burke said.

Court documents outline charges ranging from conspiracy, possession with the intent to distribute meth, and aiding and abetting the distribution of meth to tribal members. Burke said the investigation included 74 drug buys for anywhere from five to 50 grams of meth, which has spurred violent crime on the reservation.

Up to 95 percent of the violent crimes cases handled by Burke's office have some connection to controlled substances, though not always meth, officials estimated.

The joint investigation was conducted by the FBI, the Navajo Nation Division of Public Safety, the Bureau of Indian Affairs and a northern Arizona street crimes task force.

A decade ago, the use of meth on the Navajo Nation was rare. But police there increasingly saw signs of paranoia among people stopped for traffic violations, more meth paraphernalia littering the landscape and tragic cases of meth-related violence and neglect.

The tribe outlawed meth in 2005 and increased training for police. Although Navajo authorities can charge anyone for the use, possession or distribution of meth, federal penalties are much more harsh.

The tribe handles only misdemeanor crimes with penalties of up to a year in jail and $5,000 in fines. One defendant arrested as part of the federal investigation faces up to 80 years and $4 million in fines if convicted of possession of meth with the intent to distribute near a school. Most others are facing up to 20 and 40 years.

Navajo Nation Council Delegate Hope MacDonald LoneTree said she pushed for the tribal law after hearing a presentation about a 6-month-old child who was assaulted by a person using meth.

“The uprooting of these drug dealers in our communities is going to have a huge effect,” she said. “The communities on Navajo suffer greatly from drug abuse and the drug trafficking. The violent crime is something that we can see for generations because of the age of the victims.”

The drug not only is a scourge on the Navajo Nation but around Indian Country, with meth use among Native populations almost twice that of other ethnic groups.

The White House Office of National Drug Control Policy on Thursday announced an advertising campaign to combat methamphetamine use in tribal communities. Print and billboard advertisements and TV commercials will begin airing April 28 in the 15 states with the highest percentage of Native Americans.