More than 750 bogus call centre workers stole millions of dollars from American citizens by posing as United States tax officials, according to Indian police who detained and questioned the alleged perpetrators.

Some 200 officers raided seven premises masquerading as call centres in India’s financial capital, Mumbai, in a massive operation on Tuesday night following a tip-off about an international phone scam, a senior police official said.

“A total of 772 employees were detained. Out of this 70 were formally arrested and the others were released but investigations against them are ongoing,” said Sukhada Narkar, a spokesperson for police in the Thane suburb of Mumbai.

Police allege that the accused would telephone Americans and pretend to be officials from the Internal Revenue Service, the US government body responsible for collecting taxes.

They would tell the person at the end of the phone that they had defaulted on their tax payments and owed money.

After duping the victims into revealing their bank details they would then withdraw money from their accounts, said Narkar. The fraud had been going on for over a year and police believed that each day it netted around 10m rupees (£118,000/US$150,000).

“We have booked them under various sections of Indian penal code and action will be taken against these bogus call centres and their employees,” Narkar said.

Narkar said Indian police had not worked with US authorities on the case, although there have been reports in American media about similar-sounding scams, which authorities have said might be operated out of India.

India has been a major call centre hub with foreign firms using its workers for everything from answering bank client calls to reading out train timetables or delivering IT support. But India recently lost its crown to the Philippines and is struggling to maintain its share of the global outsourcing market.

Courtesy The Guardian