New York ? Colombian drug dealers are apparently using puppies to smuggle heroin.

Federal investigators believe a drug ring used dogs, as well as human drug swallowers, to conceal millions of dollars in liquid heroin on commercial flights into New York City.

Ten puppies were rescued during a 2005 raid on a farm in Colombia, the Drug Enforcement Administration said Wednesday, while announcing more than 30 arrests.

A veterinarian had stitched a total of 3 kilograms of heroin into the bellies of six pups. Three later died from infections after the drugs were removed.

It was unclear how many dogs were used in the overall scheme, and investigators do not know their fate after they arrived on U.S. soil, said John P. Gilbride, head of the DEA’s New York office.

Besides the pups and human swallowers, authorities said the Medellin-based ring also concealed drugs in body creams, aerosol cans, and the linings of purses and luggage.