The gang were so successful that Colombian traffickers were pushed back from some of their traditional territories in the US, according to officials at the Drug Enforcement Agency.

We believe we have dismantled a major heroin-trafficking organisation operating in this country

US Attorney General Janet Reno

They say the ring was operating in 22 towns and cities across the country, selling an unusually pure type of heroin, black tar, worth millions of dollars.

Investigators believe the gang brought the drugs from Nayarit, Mexico, to a command centre in Los Angeles.

From there, couriers including young girls and older men fanned out across the country to deliver the heroin to more than a dozen states.

The ring has been found operating as far apart as Alaska, Hawaii and Texas, say officials.

Authorities say the ring targeted addicts using methodone clinics

The arrests came after a year-long operation, code-named Operation Tar Pit.

"We believe we have dismantled a major heroin-trafficking organisation operating in this country," said Attorney General Janet Reno.

Officials said the traffickers were bringing in more than 30kg (65 pounds) of heroin to the US every month, which was peddled to heroin addicts receiving treatment at methadone clinics.

"This is the first time either the DEA or the FBI has ever done a major operation against black tar heroin in the US," said Joe Keefe of the DEA. "We learned a lot."

Heroin has re-emerged in our society with a vengeance, and it is more potent and more deadly than ever before

DEA spokesman Donnie Marshall

The authorities also believe they have gained vital new information about the levels of heroin addiction and the purity of the drugs in use.

"This operation, I think, shows that heroin has re-emerged in our society with a vengeance, and it is more potent and more deadly in our country than ever before," said Donnie Marshall, also of the DEA.

The investigation started when police in San Diego, California, realised that all the city's black tar heroin was coming from the same traffickers.

'Tip of the iceberg'

The operation spread to New Mexico, where 85 people had died in the small town of Chimayo after using unusually pure heroin.

"Chimayo proved to be only a single cell - the tip of the iceberg - in the nationwide heroin trafficking network managed by the organisation," said Mr Marshall.

Officials believe other members of the gang may still be in Mexico. They say details of their investigation will be passed to the authorities there.

The arrests were made in states including California, Arizona, Hawaii, Oregon, New Mexico, Ohio and Texas.