MUMBAI — The police on Saturday detained a 24-year-old man suspected of running a multimillion-dollar fraud from a network of Indian call centers, tricking hundreds of unwitting Americans into believing they owed money to the Internal Revenue Service.

Sagar Thakkar, known as Shaggy, was apprehended by immigration officials in Mumbai after arriving on a flight from Dubai, in the United Arab Emirates, where the police said he had been living since an October raid on his call centers. He was charged with extortion, cheating by impersonation and wire fraud, and is expected to remain in custody until April 15.

Mr. Thakkar’s lawyer could not be reached on Saturday.

Officials accuse Mr. Thakkar of leveraging India’s vast supply of tech-savvy, English-speaking workers and modern communications technology to earn as much as $150,000 a day at the height of the fraud.

Many of Mr. Thakkar’s nearly 700 young employees would call United States citizens, impersonate I.R.S. agents and demand immediate payment for unpaid taxes. The police estimated that he may have bilked Americans out of $100 million over the telephone.