The Narcotics Control Bureau (NCB) has busted an international drugs racket here by seizing more than 3,000 tablets of psychotropic substances and arresting three persons, a senior NCB official said on Thursday.According to the official, the gang was involved in online trading of drugs in the US and Canada."The NCB Kolkata team seized 3,161 tablets of six psychotropic substances valued at Rs 10-15 lakh from drug dealers Ganesh Pan and Sunil Agarwal who were arrested on Wednesday," NCB Kolkata unit Zonal Director Dilip Kumar Srivastava said."The drugs were sold to customers in the US and Canada through a city-based call centre Dream Advent Services and delivered via courier. Clement Phillips, the call centre owner, was also arrested," he said.The official said that the seized drugs were procured in Kolkata as they can be sold in India but are illegal in the two foreign countries.