Police in India have arrested 70 people on suspicion of posing as IRS agents to steal cash from U.S. citizens.

Authorities in the western Indian city of Thane said they were investigating another 630 people suspected of being involved in the extortion scam.

Workers at nine call centers allegedly impersonated IRS agents during calls to the U.S., according to local police commissioner Param Bir Singh. The victims were told they owed back taxes and would risk arrest if they hung up.

Singh told CNN the call center workers had been trained to speak with an American accent.

The call centers were making $150,000 a day for up to a year before being discovered. Money would be transferred by victims of the scheme to U.S. bank accounts before being sent to India.

Singh said the police had a mole inside the organization before the arrests were made, but he said the call center owners had escaped. He suspects that the fraudsters had accomplices in the U.S., but he has not yet made contact with American law enforcement officials.

Related: IRS scam costing victims $15 million

The mechanics of the operation appear very similar to those of an IRS impersonation scam that U.S. authorities say swindled victims out of more than $15 million between 2013 and 2015.

In that case, investigators suspected the bogus calls were coming from India. The culprits stole identities to make it appear they were IRS agents in Washington.

"They have information that only the Internal Revenue Service would know about you," Timothy Camus, deputy inspector general for investigations with the Treasury Department, told CNN last year. "It's a byproduct of today's society. There's so much information available on individuals."

More recently, Treasury Department investigators filed criminal complaints in the U.S. against five individuals in three states, accusing them of fleecing nearly $2 million from more than 1,500 victims as part of a scheme to impersonate IRS agents.

-- Sara Ganim and David Fitzpatrick contributed reporting.