The gang surgically implanted more than 6.5lb (3kg) of liquid heroin into the dogs. Three of the puppies died after their wounds became infected. Seven have been adopted by Colombian families.

Investigators from the US Drug Enforcement Administration (DEA) believe that the ring from Medellin would have smuggled the drugs into New York on commercial flights, for distribution along the East Coast of America.

Special agent John Gilbride said: “I think it’s outrageous and heinous they’d use small, innocent puppies in this way. It just demonstrates what lengths dealers will go to to get drugs into the country.”

After a two-year investigation about 20 arrests have made been in Colombia and a further ten suspects are being held in New York, Florida and North Carolina. A total of 53lb of heroin was seized.

The DEA said that a makeshift mobile veterinary facility was used to implant 1lb packets into the abdomens of the puppies, six of which bore long surgical scars. Had the dogs been smuggled into the US, they would have been cut open to recover the drug.

Investigators could not say whether the suspects planned to let the animals live.

The puppy implants appear to be a variation of the common practice of paying impoverished people, known as mules, to swallow dozens of drug-packed pellets made of condoms or latex glove fingers wrapped in tape. The mules take flights to Western drug markets. Sometimes they die of overdoses when packets burst in their stomachs.

Customs officials in Britain and the US have intercepted animals carrying drugs before. Snakes have been extensively used because they cannot spit out anything swallowed. An investigation in 2003 found 223 snakes with a total of 176lb of cocaine in their bodies.

There have also been cases of tropical fish carried in “double bags” — one for the fish and another for liquid cocaine.

But the use of mammals is rare. There was a case in Miami several years ago involving horses carrying heroin in their anal cavities, and an Old English sheepdog with a strange bulge was stopped at JFK airport in New York 11 years ago. It was found to have ten cocaine-filled balloons in its abdomen.

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