MEXICO CITY (Reuters) - An elite Mexican sniffer dog kidnapped five days ago was found abandoned in a Mexico City park on Monday and reunited with its police handlers.

Working on a tip, federal police found Rex IV -- a highly trained Belgian Malinois sheepdog with a string of drug hauls to its name -- tied to a tree in a park in the gritty Iztapalapa neighborhood, a Public Security Ministry spokesman said.

"When they realized the police were onto them, they abandoned him in a park," the spokesman told Reuters, adding that the dog's identity was confirmed by scanning an embedded electronic chip.

The dog, part of an elite drug squad, was snatched from Mexico City airport on August 22 while it was en route for an operation in the northern state of Sinaloa. The thieves left a black mongrel puppy in its travel cage.

Police only realized Rex IV was missing when the puppy turned up in Mazatlan airport, Sinaloa. They feared the stolen dog, which one official compared to an intelligence agent, could help smugglers find new ways to conceal drug stashes.

Rex IV was in good condition and back with his trainers, while two employees at the company in charge of transporting him and other police dogs have been arrested, the ministry spokesman said.

Rex IV is part of an elite Special Canine Unit set up in 2001 to help hunt down the gangs that smuggle South American cocaine and other drugs to the United States.

President Felipe Calderon has sent thousands of police and soldiers to northern and western states in a new crackdown on the cartels whose turf wars kill dozens each week.