ATHENS, Greece -- Colombian organized crime rings were behind a string of heists involving costly medical diagnostic equipment stolen from hospitals in Greece and another 11 European countries, Greek authorities said Wednesday.

Police said three suspects are being sought in Colombia in connection with four thefts in Greece last month.

Four out of about a dozen pieces of equipment, most of it used in colonoscopies and gastroscopies and worth more than half a million euros (US$560,000), were recovered in Colombia with the co-operation of local authorities.

There were similar thefts in the past four years in France, Germany, Italy, Austria, the Netherlands, Spain, Poland, Lithuania, Luxembourg, Croatia and the Czech Republic, said Major-General Christos Papazafeiris, head of security police for the greater Athens region.

Papazafeiris said the culprits were "mobile, organized groups of South Americans, mainly Colombians, whose members, acting on orders from Colombian cartels, visited several European countries as tourists."

He said gang members scouted out hospitals, often posing as patients, before carrying out the thefts. Stolen equipment was mailed to Colombia, and Greek authorities are in the process of organizing the return of their machines.

Greece's state health system has been hit hard by deep spending cuts imposed under the country's international bailout program.