In a major raid, over 500 employees of some call centres were detained for allegedly threatening the US citizens and siphoning off their money in Mira Road area in Thane, police said on Wednesday. The raid was carried out by over 200 police personnel, mostly from the Crime Branch, late last night and continued in the wee hours on Wednesday, they said. The persons operated from call centres in Mira Road locality, which comes under the jurisdiction of Thane Rural Police, and posed as officials of US Tax Department, which is equivalent to the Income Tax Department in India, police said. They would call up the US citizens and demand their financial and bank details, failing which they would allegedly threaten them with dire consequences, including legal action. After obtaining the requisite details from the American citizens, these call centre employees would siphon off money from their accounts, police said, adding daily turnover of such dealings was estimated to be over Rs 1 crore. Based on complaints received of these activities , police kept a tab on the call centre employees and subsequently raided their premises late last night. The process of registering offence in the matter was on, police said. Further details of the racket were awaited.